So the part I bolded is your emotional response which is irrelevant.
Tom is the current Interim Champion. That means the championship is disputed. What are Stipe and Jon fighting for? The disputed heavy weight championship?
Stipe's accolades are all fine and dandy and undisputed but the fact remains, he hasn't won a fight since the lockdowns and in his last fight he was knocked out cold and for all intents and purposes, retired, until the money fight with Jon was floated.
It's really funny because you keep talking about contracts as if the UFC can't on a whim change up fight schedules as they have dozens upon dozens of times before. They've shuffled fight cards the literal night before the even multiple times, like they did for what was supposed to be Khamzat vs Diaz. There were no injuries that caused the shuffle, just Khamzats fatass, so this cope about "But the contract is signed!!" is not only beyond moronic and irrelevant to the discussion of who Jon should actually fight, it assumes an internal legal understanding of UFC contracts, which I guarantee you do not, and assumptions about the ironcladness of these contracts (hint: they're always in the UFCs favor). Tom wasn't even supposed to fight for the belt, when Jon got injured, it was supposed to be Pavlovich vs Stipe, wasn't it? I mean, he was signed as the alternate, in camp, making weight. He was signed to step in if someone was injured specifically. What happened? Stipe noped the fuck out of there because he's there for a money fight with Jon and nothing else.
This is the cope of Jon's fans. Their hero has to ride out into the sunset, fighting Old Man Stipe and pretending it's this career solidifying win, clutching at kleenex through tears of joy "I can't believe he's really gone and done it and proved he's the goat sniffsniff"
Tom represents what Jon has feared the most, what his fans fear the most, the thing that rings so true in this sport, that most men go out on their shield and not their throne. Jon saw it happen to Stipe in his last fight, which is why he wants to pick at the Bones and call it a career.