We do, but they only contribute a small portion of the world's energy. It will take a long time to get to a point where most energy generated is renewable, and by that point, the climate is going to be a much much bigger problem.
- We might be sitting at a 500M population after the [climate / pandemic / AI / nuclear / system collapse / etc] apocalypse.
- We might be sitting on a terraformed Mars (or in bubbles under the ocean)
- We might be sitting in glass domes in the middle of an increasingly climate-hostile Earth
... and so on. We're very bad at predicting the future; it's hard to pick from thousands of (individually highly unlikely) possibilities.
Admittedly this isn't true of all possible scenarios. And in some, longevity would be really helpful.