If people knew they would live for millions of years, I'm confident some of them would get around to changing their policies a bit to allow for some gradual changes.
I think you're underestimating the force of habit.
Also, when you do the same thing for a long time, time itself changes. A million years relative to our psychology would not be anything like a million years relative to million-year-beings'.
We only need 0.01% of the population to make changes, and not very fast, and they will eventually transform the world to the point it's hard for others to ignore.
