Because he's being treated like crap by fans and media alike. He's become a joke and a punchline, despite putting up some of the best numbers of his career. His numbers are near identical to his ones in the second year here. And yet, still, 0 respect.
There's no denying that Luongo is an amazing goalie; I would be ok with keeping him over Schneider provided that we got something out of the trade.
However, being the key player on the team means that reactions toward him will either be highly positive or highly negative. This is not a unique case in Vancouver, it is the same for any franchise in any sport.
None of this ultimately matters as the media and the fans aren't responsible for roster decisions. It comes down to the front office choosing between a proven but faulty veteran against a cheaper, and equally talented upstart.