That was 10 months ago. And while being treated like a god has its benefits, it also comes with negatives. When people don't get what they want, people spew venom at gods. The way this fanbase treats one of the best players that has ever worn the jersey is embarrassing. That's what's absurd. That and the idea of letting him walk in UFA. Wanting to be treated fairly does not equate to wanting to leave, and it should not equate to having to.
He got paid for what he did on his ELC, consistent with history, and he outperformed his contract. Now, he's going to sign another contract that he will likely outperform. He owes you nothing.
That elite player has helped this team more than you realize. How quickly people forget how much worse it can get.
I credit GMs when they do good things that improve my team, and criticise GMs when they do bad things that hurt my team. Letting Marner walk in UFA would be a horrific things that would hurt my team a lot.