Yc founder, there's not really any pressure like this that exists. Basically i think it's a proximity thing and consistent exposure to a specific section of the startup world that makes this happen.

Basically all those people would go all the same networking events sponsored by yc. There's not pressure so much as these people all have frequent and paid for, opportunities to "hang out" and talk about tech stuff together. Its possible you could define this as "pressure" but I think it's more of who you hangout with rather than some top down implicit force.