Ask HN: Why some startups are using AWS?

Or essentially: why someone who presumably knows what he's doing, is using AWS? I understand why the clueless do, because it's so convenient and Amazon marketing power is so strong - i had clients who had no concept of a dedicated server in their heads: for them it was either AWS/GCP/Azure, or buying a server and putting in their office - Amazon pushed other alternatives out of their brains with their marketing power - but the startup founders should still understand?

With AWS or any cloud you overpay 5x-100x. Why anyone rational would do it?