The differences are as follows:
(1) Chonan was not in the UFC so there was no way Anderson could have rematched him. Struve is in the UFC right now and has been the entire time Stipe has been in the UFC.
(2) Chonan beat Anderson outside the UFC. Struve beat Stipe in the UFC.
Stipe is on his way to become the HW GOAT, maybe the actual GOAT. From a historical perspective, it's going to lead to pesky unanswered questions. If Stipe is the GOAT, how come Struve beat him? Why didn't they rematch? Was Stipe ducking Struve?
We may know the answers to these questions now but over time the context of these answers will fade away and the questions will reemerge.
Plus I just want to see the rematch. This is MMA. Shit happens. Even though shit happens ALL THE TIME some are stubbornly closed off to the possibility that shit will happen again.