Because in the current market you can get yourself a better lifestyle burning through VC cash than by trying to get that cash from the paying customers.
And even if you fail you write some blog posts, do the speaking circuit and end up with another high paying role in a startup, VC or a services company (Government, Co-working space, law firm...)
I thought the expectation was for VC funded CEOs to take low salaries. How often do they sell equity in fundraising rounds and/or take decent salaries (500k+)?