It's because they are utterly fucking clueless. The majority of football fans, are completely clueless. They won't realise it until it's too late, and we've lost another half dozen games, maybe even finish the season 15th. Yet they still will find excuses for Ange, say back him in the summer, give him next season.
If people cannot see the many many reasons why Ange should be sacked, and that another manager could do far better with this current squad, then they never will think he should be sacked. For them, it's injuries, lack of backing, always anyone but the manager etc
It's pointless debating with them on twitter, they are all just dumb as fk.