Most non-startup jobs tend to be well-defined and come with a pre-existing business strategy and existing resources, such as a project codebase and existing at least semi-working solution to which one can inspect and add to.

Contrast this with startup companies, where it's often required to explore and build completely new things from the thin air of the ether. I'm not saying other jobs don't also have elements of this, as new projects and opportunities do emerge, but being at a startup is definitely an extreme situation and arguably a different game. In the meta lens, it can be viewed as the act of mining the veins of market realities for golden ideas.

It's for the risk takers and adventurers. I've witnessed many a great engineer learn it's too undefined which can be uncomfortable, and is not a good fit for them.

It's nothing personal, along the exact same lines as some folks who can't stand working for a large company.

Different strokes and all that. This form of diversity is one of the beautiful things about the spectrum of humanity. In aggregate, it works!