It's because Morrissey had the most extraordinary emotional and psychological impact on so many young(ish) people back in the 1980s and 90s and if someone has that impact on you in your more formative years then it's insanely hard to just...let go. So instead of simply stopping buying the new records and going to the new shoes, these people take out their frustrations on a site like this.
(I'm not having a go, I'm unable to move on myself, despite finding some of his utterances and apparent beliefs completely at odds with my own!)
It's because most of the Moz diehards have never separated Morrissey the artist from Morrissey the man. We were never meant to; diarising his life through song is what built the Moz 'cult of personality'.
Now, you've got a whole bunch of people who are totally disillusioned with the man but can't drop the artist because he's still got that fantastic singing voice & he CAN still be a great songwriter. So many 'irregular regulars' are waiting for that glimmer of greatness. The whole thing is also cyclical - how many people wrote Moz off and then came back on board after
Quarry? How many came back on board after
Dog? A lot.
Personally, I got off the "Moz bus" around the time of
World Peace - I found it unlistenable and just thought "what the utter f*** is this?" to everything he was saying and doing. LIHS was equally awful. Then, bizarrely, I heard an off-cut like
Blue Dreamer's Eyes and I'm back in. Moz is never, ever more than one great song away from being back to glory with his fans but sadly his own mouth has done a lot of damage to his career.
Also, Johnny Marr's public profile has skyrocketed in the past year - not only drawing more attention to the Smiths but to the enormous 'ghost' he has behind him. Look at ANY Marr clip and there are dozens of people commenting below to say "God, if only Moz was singing...". Even people who hate Moz. That's a hell of a legacy.
TLDR - cult of personality + he's still talented + untouchable Smiths legacy