Aldo wanted to but was not allowed to compete for the LW title while he was FW champ.
Pitbull was denied a crack at the LW title while FW champ. Bader is allowed to go after a second title though.
Conor was allowed to compete for the LW belt while FW champ but was then stripped of his FW belt.
DC might be allowed to keep the HW title and wait for Lesnar in Jan and defend his LHW title in Nov.
Look at guys like Elkins who win and win and never get anywhere and guys like Faber who get title shots every weekend. Or how Ngannou was fast tracked to the title and guys like Maia had to wait and wait for their shot.
Look at how thousands and thousands of LW and WW men fight for a crack at two titles while a few handfuls of women get to compete for four titles.
Thats the thing about prizefighting in a situation where the promoters control the titles. It gets ugly sometimes and competitive sport part gets trashed for the prizefighting component.