Because startups are based around abusing their employees who don't know better. If you aren't a founder, you are nothing. That's a tough pill to swallow but i

Because startups are based around abusing their employees who don't know better. If you aren't a founder, you are nothing. That's a tough pill to swallow but it's a good thing you realized it and are doing so now, rather than after you took the job as first engineer. Your insight is 100% correct. You, as the first engineer, are taking on a huge amount of the risk of the startup and the work but you aren't getting the upside like the founders are.