What's so unwarranted? Here's Brock Lesnar, who has been given the world by the WWF because he's huge and sort of wrestles well, pushed over every guy on the roster without doing much at all to deserve such a meteoric rise compared to the efforts of let's say a Bret Hart or a Steve Austin, then he walks out on it all, making his entire buildup for naught. And to top it all off, his final match is a pile of shit. When a match is that bad, all hate is warranted, to say nothing of anything else that transpired prior to the match.
Everyone was pissed because they knew how this would work out. Nobody thought he could cut it in the NFL, it was painfully obvious. He'd leave, he'd try, he'd fail, he'd come crawling back begging for a job when he runs out of money. Lo and behold, he left, he tried, he failed, he came crawling back for a job because he ran out of money. Search the Internet; I'm sure everyone even detailed the whole course of events.
Brock Lesnar did nothing to make me wish for his return. He didn't do anything as compelling as Shawn Michaels, Bret Hart, Steve Austin, The Rock, or HHH ever did with their title reigns. He just kinda grunted a lot and fell on his face. I don't care if the Neckless Wonder ever comes back.