For me it's almost certainly the risk to mental health - a lot of founders I know are chronically stressed, anxious or lonely, even the ones doing great work.
--No contracts of my own
--Fear of litigation/overhead costs
--Easier to just work for someone else's shop, I have bills to pay
Risk aversion given that I have a good job that I worked for 10 years to get.
Sufficient contacts or "network"
Potential customers, employees, support services, mentors, people to run stuff by...