Because you could get a similar and higher-paying job with zero risk by applying to one of the bigger companies.

I'd definitely contend that a job with a bigger company would not be 'similar'. I previously worked at a "bigger company" and the job was utterly miserable. The startup I work for gave me stock in the company, but I wasn't actually expecting it- I would have worked there anyway.

As long as you're getting decent pay I see no reason to stay in a miserable corporate job if you don't want to be in one.