It’s more complicated then just sheer dislike of Zverev by some.
In hindsight the Dimitrov match prepped Zverev enough. As he was down a set and setpoint against in the second and cameback, it let him loosen enough for this match with Sinner. Of course it doesn’t always work that way.
I give the Crown Prince credit for climbing back to the top ten ( on the ATP live rankings) after that terrible injury last year. I had my doubts he could recover enough but age 26 he’s clawed back, so respect for that.
The problem with him since he won his first Masters at age 20 is the expectations were, fair or not, that he could jump up to the final level & win Majors. This has not happened and his game hasn't matured/improved to the point where IMO he can challenge Alcaraz ( who is still developing) or Novak ( who is still a level above him) at a Slam.
In contrast, Sinner is an up and comer , & again fair or not, the hope is he can leap through through that Slam ceiling. So losing to Zverev disappointed those who want to see any other young player reach his full potential and breakthrough. Mens tennis needs that. Zverev is staus quo of an also-ran who consistenrly falls short in Slams.
Zverev winning is to me more a measure of Sinner falling short with a huge opportunity in front of him ( the cramps did not help) and especially in a Slam where he was mentioned in the same breath as the big boys as a favorite.
People act like these kids have forever, unfortunately by age 23 if you dont break through after 4 or 5 years on the tour to at least reach a Slam final the odds are its not going to happen.