Because not everyone is a smart and talented overachiever like you. Some of them just want to find themselves in a comfortable situation, with the least amount of work necessary.

When "normal" people bail out on a startup, they go find a regular job because they have to. If there was an option to just live at the other's expense, they'd just go on to do it.

Also, the 21% percent of people who say they would start a company, but don't, are probably more afraid of the possiblity of failure than unable to cope with the consequences.