Well what do you want us to do? Yes, Garoppolo didn't do his reputation any harm with his appearance, but we're fans. From a fan perspective what Brisset did was simply more impressive than what Garoppolo did, especially considering how green Brissett was, so as a fan, I'm actually more excited about Brissett.
There's also the fact that we're going to keep Brissett and he's going to be the guy right behind a 40 year old starter. Bracing for the departure of both Garoppolo in the next few months in all likelihood, as well as Brady in the near future as well, we need to see good signs about Brissett, because he's about to become the primary backup. So fans are (or at least I am) excited about the fact that Brissett did as well as he did.
You've also got fans bracing themselves for the departure of Garoppolo and struggling with the fact that we're going to have to say goodbye soon. That just makes it all the easier to pump Brissett's tires because after all, if Brissett is great, we won't wind up missing Garoppalo as much.
Lots of reasons to shift the conversation to Brissett just now.