I'm curious as to why startup would be a goal specifically vs the job itself at any company? Lifestyle, company size, career growth, equity, something else?

You have a lot more control in an early stage startup vs a later stage one where lots of design decisions have already been made before you arrived and you're kind of stuck with them. If you like having an influence on the design of the product, tools, even implementation languages the earlier you get in, the more influence you have.