I would speculate the main hurdle was probably believing the players in the first place. Humans are notoriously bad at not-noticing-patterns in properly random data. And statistical bugs like this require more effort and careful attention to detail to reproduce than deterministic bugs.
Another hurdle is likely that game developer culture strongly favors integration testing over unit testing. Games are optimized for fun, not correctness, and you can't unit test fun. This specific roulette selection function would have been straightforward to unit test, and a unit test would have caught the distortion. But now imagine people keep varying how important distance is to the calculation in order to make it "feel right". Updating those unit tests is suddenly a noticeable slowdown on how quickly you can iterate on game feel.
Yeah, WoW had many many problems with people not understanding probabilities that they added explicit code to track all drop rates and compare them to intended - and actually found a bug or two that way.
But mostly it was to explain to people that a 1 in 100 chance doesn’t mean you’ll get it even after 200 goes.
Another hurdle is likely that game developer culture strongly favors integration testing over unit testing. Games are optimized for fun, not correctness, and you can't unit test fun. This specific roulette selection function would have been straightforward to unit test, and a unit test would have caught the distortion. But now imagine people keep varying how important distance is to the calculation in order to make it "feel right". Updating those unit tests is suddenly a noticeable slowdown on how quickly you can iterate on game feel.