I don't know if it's YC specifically who 'care' as you say. If you see the launches : https://www.ycombinator.com/launches

There are an ungodly number of AI based submissions, if the pool consists of for example 80% AI based, it stands to reason YC will probably be choosing between a lot of AI tech. Almost like survivor bias.

If the new trend of submissions is AI, I don't see why YC should say : "No we want to improve humanity" . Doesn't seem like that's their interest really.