I think the club may be thinking "Can we afford to keep him in the long run?"
If, for talks sake, 500 paying customers from this season decide not to go next season, that's more than £10k per home game. Over a season that's an awful lot of money and would pay for JC's wage in itself. Obviously I'm just speculating about figures etc but there are loads of unhappy fans, and of course not all who threaten to stop going will, but can the club take that risk? I honestly don't know, just trying to think how the club may view things, but I think saying "we can't afford to sack him" is perhaps too simplistic. There's also the whole "what happens behind closed doors" scenario, maybe the board think it is time for a change for change's sake. And of course, this could all be a lot of pish and JC is already planning for next season... we'll find out soon enough I'm sure.