firstly may I point you towards the anime and manga stack exchange where this question may find answers from people with more specific knowledge of Dragonball.
To answer your question though you have to look at 3 quick points:
The Current Stakes
This is the most important reason in my opinion. The entire universe will be wiped out if they lose. That includes their
Otherworld (which Frieza is a part of). It is in their best interests to
bring the strongest fighters to give them the best chance of survival. Frieza can hate Goku and the other Z Fighters, doesn't stop him needing to work with them to survive.
His "guards" for the 24 hours of his revival
Frieza has spent all his time currently either with Goku (who thinks he can control Frieza), or around Beerus (who can certainly destroy him). This doesn't leave much space for Frieza to be the Evil Emperor we know he is. When he is involved in the Battle Royale, he is being watched by Zen-Oh who can erase universes, and will wipe him out if he annoys him.
Who would you pick instead?
Frieza has "Golden" Form which leaves him as powerful as SSJB Goku (at least at the time of their fight). Who else is at that level? We don't know if Cell has had the chance to continue training in the Otherworld. It seems Frieza wasn't able to when he first went to the Otherworld - and yet he claimed he had mastered the energy requirements of Golden Form when he was sent back the second time.
Other than Cell (who if he hasn't trained can be beaten by a SSJ2-power fighter), and Buu (who is out of action) can you suggest a replacement?
Edit: as a final point, Goku is still naive and focused on wanting to fight the strongest enemies. He has let a tired Caulifla and Kale escape during the Battle Royale so that they can get stronger before he has to fight them. He may be hoping that Frieza gets stronger during this fight and he gets an excuse to fight him during the Battle Royale or at some point after (if Frieza gets his wish to be revived by the Universe Dragonballs).