Why did Darth Sidious wait to execute Order 66?

Question

The First Battle of Geonosis occurs near the end of Star Wars: Episode II - Attack of the Clones. There's a scene in the execution arena where the Jedi are surrounded by the droid army. Dooku offers the Jedi a chance to surrender so that their lives are spared. The Jedi refuse, and at the last moment before they are destroyed, the clone army shows up and saves the day.

If Darth Sidious's goal is to eliminate the Jedi, then why didn't he execute Order 66 right then and there at the First Battle of Geonosis? The Jedi were surrounded and surely would have been destroyed. Even Yoda was on one of the ships carrying in the clones. Why did he wait 3 years to give Order 66? Surely he didn't require any sort of bureaucratic permission: in Episode III, Darth Sidious simply gives the command ("Execute Order 66") and the clones comply ("It will be done, My Lord").

It seems possible to construct plausible reasons why Darth Sidious might have wanted to wait:

• Sidious was waiting to lure Anakin to the dark side.
• Some Jedi may have stayed behind instead of going to Geonosis. Those Jedi would have continued the fight against the Sith.
• Palpatine was worried that the Senate was still too strong and might turn on him.
• Palpatine wanted to build up the clone army to even larger numbers, and continuing the war was necessary to achieve that goal.

But what is the actual evidence that the movies themselves provide?

Note:

This question was posed here, but the answers are not completely satisfying for someone looking for a movie-based explanation. The list of possible explanations (above) draws heavily from that scifi thread. But here are the more specific issues I have with some of those answers.

1. The first answer, which was accepted, cites the novel Star Wars Republic Commando: True Colors.
2. The second answer, which was the most upvoted, states: "he was able to use the Jedi as tools to help eliminate those that stood in the way of his ultimate goal," but I'm not sure which specific people from the movies this is referring to.
3. The third answer states: "One more reason: Order 66 works because the Jedi have come to trust the Clone troops implicitly. This trust would have to be built first." But this doesn't address the fact that, in the movie, the Jedi were surrounded by the droid army and had all but been defeated. Giving the code at that time would have eliminated the Jedi, assuming they were all at the battle.
4. Another answer states: "Simply, Palpatine didn't want to lose Anakin. Even if Anakin would have been isolated from Order 66, he would never had gained loyalty of Anakin. And, Anakin would have turned against him for killing Jedi." But Sidious would want Anakin in order to achieve his top priority of eliminating the Jedi and gaining total control. If he executes Order 66, then now (a) the Jedi are all gone, (b) he has a massive army of both droids and drones at his disposal, and (c) an assistant (Dooku) who is extremely powerful. His goal is achieved, and there's no need to use Anakin as a means for that goal.

Answer 1

At the time of the Battle of Geonosis, the Jedi were revered as peacekeepers in the Republic. If Sidious had ordered the deaths of all the Jedi on Geonosis, he would have revealed himself as an enemy of the beloved Jedi who murdered them in an act of open treachery. His public image would have been terrible. Yes, he'd have control of both the clone army and the Separatist droid army, but all the people of the galaxy would be united against him. Sidious would have had to rule by fear, but his armies would not be sufficient to do so -- for that he needed the Death Star, which would not be completed for another few decades:

[Tarkin]: The Imperial Senate will no longer be of any concern to us. I've just received word that the Emperor has dissolved the council permanently. The last remnants of the Old Republic have been swept away.

[Tagge]: That's impossible! How will the Emperor maintain control without the bureaucracy?

[Tarkin]: The regional governors now have direct control over territories. Fear will keep the local systems in line. Fear of this battle station [the Death Star].

_{Star Wars Episode IV A New Hope script}

In order to cement his rule over the galaxy Sidious needed to discredit the Jedi in the eyes of the public and then execute them so that Palpatine could be seen as a benevolent ruler who saved the Republic from the treachery of the Jedi. Hence Palpatine waited until the Jedi attempted to arrest him when they discovered he was a Sith Lord, after which he could credibly accuse the Jedi of treason for attempting to take over the Republic by assassinating the elected Supreme Chancellor of the Republic.

The Clone Wars also served to make the Senate and people of the Republic weary of war and willing to do anything for peace. In Palpatine's speech to the Senate in which he announced the creation of the Empire, he mentioned that

In order to ensure our security and continuing stability, the Republic will be reorganized into the first Galactic Empire, for a safe and secure society which I assure you will last for ten thousand years.

_{Star Wars Episode III Revenge of the Sith script}

Whereas the Republic was too weak and ineffectual to prevent the Clone Wars, a strong Empire would ensure that the galaxy would enjoy peace. That is how Palpatine justified the transformation of the Republic into his totalitarian Empire.

Answer 2

There are a couple of reasons why Darth Sidious didn't execute order 66 at the First Battle of Geonosis:

1. He was waiting for all the Jedi to be in different places. That way they wouldn't have time to gather quickly and coordinate any counter-action.

2. He sent all the Jedi to different places where warfare was already underway so they could be killed more easily. Consider the idiom "United we're strong" to understand his "divide and conquer" tactic.

3. Chancellor Palpatine needed a reason to execute order 66 so the senate would be in his favor. Eventually, Mace Windu's attack gave him that reason and the sympathy of the senate.

   PALPATINE: . . . and the Jedi Rebellion has been foiled.

   BAIL ORGANA: I was held up. What's happening?

   PADME: The Chancellor has been elaborating on a plot by the Jedi, to overthrow the Senate.

   BAIL ORGANA: That's not true!

   PADME: He's been presenting evidence all afternoon.

   BAIL ORGANA: And the Senate will go along with it, just like they always do.

   PALPATINE: The remaining Jedi will be hunted down and defeated. (applause) Any collaborators will suffer the same fate. These have been trying times, but we have passed the test.

4. He waited those years so the Clone Wars could reduce the number of Jedi.

5. He was planning to make Anakin his apprentice. If he had executed order 66 beforehand, he would have lost Anakin.