The situation is that many, many employers make signing one of these a de facto requirement for employments, and they are widely known / believed to be unenforceable, but you still default to being on the hook for your own legal defense if a company that has otherwise idle full-time lawyers on their payroll and someone high enough decides they don't like that you and a bunch of other people quit. They weather that fight better then you and your startup will.

I worked at an SaaS offering for market research surveys that was threatened with a lawsuit because we hired a software engineer who used to work phones in a call center that specialized in polling people. He signed the non-compete contract, obviously, but the point was to discourage him and other people from quitting, or their potential employers from hiring them.