At the end of X-Men 2 (2003), when they're trying to escape from the flood, why didn't Nightcrawler, teleport everyone to a far place?
There wasn't time.
Although Nightcrawler's powers aren't really covered very well, in the movies he is limited as to the amount he can carry at anyone time, usually this is one person.
He'd have to grab each person in turn, teleport them away, teleport back, grab the next and continue repeating until they were all away.
This would have taken too long as there were a lot of people to transport and the physical toll would likely have killed him.
Nightcrawler is able to teleport to any place, as long as he knows where he is going. His teleportation gives him the appearance of being vaporized into a very brief puff of blue or pure black smoke or gas wherever he teleports to or from. As a teenager, Nightcrawler could not teleport mulitple people without risk of extreme exhaustion or fatigue.
Of course, out-of-universe, it's because Jean holding back the water is much cooler.