I think the answer falls into two categories: #1) Startups that don't apply 'cause they just don't want to #2) Startups that don't think YC would accept them

I think the answer falls into two categories: #1) Startups that don't apply 'cause they just don't want to #2) Startups that don't think YC would accept them #1 is fine - if you don't want to do something, don't do it #2 is silly - let YC reject you; don't reject yourself (regardless of location, stage you're at, one co-founder can't make it, idea, etc.)