Many reasons. You're taking on a risky business venture. You aren't getting a comparable salary that you could obtain at another company. You don't know if it

Many reasons. You're taking on a risky business venture. You aren't getting a comparable salary that you could obtain at another company. You don't know if it will help, hurt, or be neutral with regard to your future career prospects. A startup is going to more demanding and stressful, and a bigger drain on your life outside of work. You could find yourself pushed out for unfair reasons, while you made legitimate contributions. If the startup fails easy on, you likely won't be eligible for unemployment benefits. All of these risks should be accounted for when considering your compensation. If you can't accept giving up equity to people who will not be around when the company IPOs, then expect to pay a full market salary with benefits.