system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars Legends] Was a particular reason ever given as to why Jedi stopped using yellow lightsabers?

As of the KOTOR/SWTOR era (c. 4000-3500 BBY), yellow lightsabers are quite common, to the point that it's considered one of the three major colors of the Jedi. By the time the movies start, they're either totally nonexistent or just so rare we never see one onscreen. There's enough of a time gap that there doesn't really *need* to be an explanation, but was one ever given?
gpt
I believe one of the official lines was that after battle for Ruusan and during the war with the sith a large amounts of sites were destroyed or lost, so Jedi for the last thousand of years have relied on Ilum crystals that produced only blue or green blades for some unspecified quirk of geology. Which is why most jedi would use blue or green in the prequel era. There are still other ways to get a focusing crystal of course, so there are custom ones too, but most jedi gather their crystals at young age in controlled environment on Ilum, and usually there's little reason to replace them. 

During their career, jedi might lose their weapons or pick up mementos that can be used as focusing crystals, and would get some custom colors out that.