True, the means of their transmission is known but somewhat random. True, there is being unpleasantly ill in the aftermath. True, the government really minds if there are supers it can't control and isn't too fond of having many that do obey.
But I think the additional effect of having powers going haywire immediately afterwards are not enough to explain why power-chasers don't exist in great numbers -- or great success. Immunity, perhaps? 'cause the sorts of idiots who would think "SUPERPOWERS! Where's MINE?" would not be moved by any consequences I put in. Comatose for life? Nah, I'll be the LUCKY ones.
Which would really move the story away from what I want.
Perhaps power chasing creates immunity -- bwahahahahaha.