There are plenty of politicians who have played the long game, also political parties take actions on longer time scales than individual politicians. Stances that politicians take on issues often come down from the party anyway. Many politicians don't care about many issues, but they vote based on their party's stance. The blue party is staffed with all types of people, many of whom will live to reap the benefits of changed demographics.

Heck many politicians are still in office 18 years later! Look at Nancy Pelosi, she was in office for 38 years. That's multiple batches of anchor babies.

It's not that long of an investment. We have seen this entire country go from 99% white in most places to below 50% in most places, in ONE generation and that change is clearly visible in national elections.