I'm sure you can guess - pure risk aversion. Your business idea is risky enough, and they would need engineers to assess your (possibly ever-changing) DIY stack.

You see the same thing in the corporate world for in-house stuff. Your manager (and your manager's manager) don't want to hear about in-house or self-hosted things that AWS can provide.

This is totally understandable. It's a repeat of the whole "nobody ever got fired for buying IBM" mantra of computing's early decades.

It also totally sucks.