Features, userbase, talent; the same reasons a developer or engineer would work with any company.
Let's play a game; how many degrees separated from Facebook is HN and YC? You go first, take a guess!
Let's play a game; how many degrees separated from Facebook is HN and YC? You go first, take a guess!
Let d:(x,y)->n be the degrees of separation between x and y. Since d(x,y)=0 implies x=y, and we know that FB and HN are not identical, we have d(FB,HN)>0.
Then, since d takes integral values we know that d(FB,HN)>=1 in any case.
Your hands aren't clean here, if you actually cared about avoiding Facebook at all costs, you wouldn't be here. The fact is, you don't (nor should you).