My reply was going to be "that's not their core competency" until I read your last sentence and realized "well, YC is probably better at this than the companies they fund doing it individually.."

Alternate theory: it's important for a young company to practice things like finding office space, figuring out coffee machines, building independent team culture, learning how to recruit, filing state taxes, etc when they are early and mistakes are easier to fix.

Good companies are not just the product they ship.

Make that part of the YC process. Mock renting of space, filling it, etc. Have reviews of how they did, things they considered, etc.