Mainly because of the hype/marketing, but I may be overestimating it. It’s a good point that Avengers bombed, but I do think Rocksteady is a more competent developer than CD (I’m not personally a big fan of their Tomb Raider games).
I also just tend to think anything is possible until it isn’t. It wouldn’t be the first game to buck expectations if it somehow managed to be a hit.
Either way, the fact that this is the only game Rocksteady releases in nearly 10 years will be a deep source of bitterness.