From anecdotal evidence, it is the fact that persons who’ve been reported continue to show up in races and results that I believe lead many to think nothing happens. I could be wrong.
You probably don’t need to clean up the user base, instead just make real racing (as opposed to fondos etc) a different level requiring more disclosure regarding mass and height, much like in RL anyone can enter a fondo style event but to enter a national body approved event you need a license. You could possibly have different levels of disclosure so the top level requires weigh in videos etc (like https://www.ebiopassport.com/) while the lower level just requires mass and height visibility so any extreme changes can be monitored.