I think a part of it for this game in particular is the multi-job characters.

For instance i main healer so my diamond gear from raiding is healer stuff
I play mage and tank a lot in more casual settings so my tomestones ended up going towards those
I wanted to try out SAM since it doesn't have as much of the current things i dislike about melee dps so my ridorana gear has been going SAM

not perfect but can kind of see how having all kinds of sources helps gear out several jobs simultaneously