Except Jon Jones said more than once he wanted to vacate the HW belt, that obviously if he thinks in retiring, he won't take the belt of a division and no one can have it because someone retired with a belt. He has said many times he'll retire. But... The UFC doesn't want someone that is still, perhaps, the fighter that could beat the most two dangerous other guys, Pereira and Aspinall, to retire. They want to $ with fights. And Tom is just hiding his true wishes when he said "if JJ doesn't want to fight, ok, vacate the belt"... He knew he didn't want that to happen though, because he kinda realizes that without Jon Jones there, his division seems totally dry, uninteresting... And also, Tom would likely get in all fights there at HW as much as he could make fighting JJ once. Tom even said once he wants to be dominant for some time, but that he won't retire too late, that one of his goals is also to get good enough $. So ofc he says "ok, vacate the belt" while crossing his finger JJ doesn't do it... He says it just as a way to give more authenticity to the desire of wanting to be the champion as opposed to the desire of fighting Jon Jones.
If anything is holding up the division, it sure is not Jon Jones, as he had made clear after Stipe, the belt could be free. It wasn't though because Dana and Tom want badly that not to happen. That's why Aspinall also says "I'll retire Jon Jones without even fighting him", it's his way to touch on Jon Jones' ego and competitive nature, to appeal to Jon Jones desire to "man, I want to shut this kid up". So there is your answer.
It seems though that Jon Jones also really wanted this fight, and instead of calling his opponents and showing confidence like he always does, it's totally possible he saw that acting in a "weird" way would be the way to fill the arena, ppl gotta believe strongly that he'll lose, so JJ's promotion way, hypothetically, could all have been this kinda attitude planned out...