I don't know how other investors operate but if YC sees a good founder working on something they don't care about, just because they think investors want them to work on it, they'd almost certainly tell them to switch to something they do care about.

pg's most frequent advice to founders about ideas is to ask themselves what they themselves wish would exist, then make that—i.e. solve a problem you yourself have. Another thing he and Jessica say a lot is that you need to be passionate about what you're working on in order to make it through the arduous haul of a startup.

That's even more true of the 'moonshot' startups, since they're harder and take longer. If you look at the hardest startups YC has invested in, you won't find many founders who aren't personally obsessed with what they're working on, and have been for many years. That's one of the things YC would be looking for before funding somebody to work on such things.