OK, so apparently, according to Tom Aspinall, the UFC had plans to match him and Stipe for the UFC 300 in April, but Stipe turned it down.
Shame, because it would be an interesting fight, but we all know who will win it and so does Stipe.
I can't really blame Stipe though, he probably has one more fight in him, so will be going for the most profitable option available. And if he loses to Jones, he could still be matched with Aspinall later, but if he was to lose to Tom, Jones will not want to fight him anymore.
Source:
https://www.mirror.co.uk/sport/other-sports/mma/tom-aspinall-stipe-miocic-ufc300-31958493"While we are talking about Stipe Miocic, my manager was contacted by the UFC asking if I’d like to fight him on April 13th," Aspinall tweeted. "I, of course, accepted. A little while later we were told that Stipe doesn’t want to fight me, and he is only interested in fighting Jones.