What do you define as “risk” and “screwing up”?
As an academic, your reputation starts the second you start putting yourself out there and publishing research and your own theories. If you screw up, you also screw up for your faculty and department who will be less likely to lend you support in the future. When you are leading a group of researchers with sometimes millions of dollars worth of funding who have deadlines and expectations, a screw up is costly on many levels.
To say nothing about the repercussions on a personal level. I still have a wife and two kids to support. The longer I’m in grad school, the longer I have to begin supporting them.
Going against the grain in your field, putting your heart out there, summoning the courage to stand by your ideas and theories requires more courage and risk than I’ve ever known.
I worked in the corporate world. Just making it into grad school required more work and effort than I had ever put into my desk job. Particularly emotional investment and patience combined with faith and hope.
To say that all graduate workers and academics have very little to lose is short sighted to say the least, especially from someone who has experience in graduate work.