Just a hunch, but I suspect the majority of those expressing that sentiment are people who decided well ahead of the film's release -- based on advance reports and fan polls which were neither especially accurate nor particularly honest -- that they "hated" it so much that they never, in fact, got around to seeing it at all.
No, I saw it. And I hated it then.
It's a lazy film. It repeats most of the plot points and set pieces from ST09. Kirk is too foolhardy to be Captain and learns how to be responsible...
again. He does another space dive sequence...
again. Spock loses his temper and starts beating someone up...
again. Leonard Nimoy has a cameo as OG Spock...
again.
And then at the end it starts regurgitating the ending of TWOK, only in reverse, not realizing or caring that Spock's death in that film was so touching because of all the shared history that he and Kirk had. The new guys barely knew or liked each other. Plus, there's absolutely no point in doing a poignant death scene when you're going to reverse it 15 minutes later. Yeah, they reversed Spock's death, too, but when they killed off Spock in TWOK, they actually
meant it.
The magic blood stuff, the interplanetary transporter, taking the ship underwater for no reason, the gratuitousness of Alice Eve stripping down to her underwear for no reason, the pointlessness of them pretending that Benedict Cumberbatch wasn't playing Khan in the entire leadup to the film, the 9/11 parallels... It's just an aggressively dumb movie.