This seems like a broad generalization, like asking “Why do junior programmers make so many bad decisions?” Your 2/3rds estimate comes from what sample size?
Organizations in general tend to risk averseness, for usually obvious reasons. Stability, consistency, continuity, security all form part of a larger scale view of the business as a whole that perhaps seniors have internalized and juniors have not. Certainly bureaucratic friction and resistance happen, but so do poorly thought-out ideas and change for its own sake, or to relieve boredom with the day-to-day drudgery that describes most programming jobs.
Ask this again when you have 20+ years experience and have lots of stories of dumb and risky failures to tell.
