It's scary to think that Kroenke has taken Arsenal down to almost midtable from being one of the top 2-3 in the league.
It worries me that the Glazer's would oversee this decline at United too
I think there are two very different cases here.
Arsenal have been bogged down thanks to their fanbase as well. The impatience in getting rid of Wenger (when it's obvious that he was doing a decent job with the resources he had), emery (who was sacked thanks to some ridiculous signings) and the blind worship in Arteta by a majority of their fan base. Most managers get sacked when they lose atleast one of players or fans or board and another section among these three is on the fence. In case of Wenger - it was fans losing patience and players were hardly enthusiastic about working for him. Under Emery, think it was all three. Whereas, under Arteta, its just a section of players who've lost faith in him. A lot of their vocal fans love him, board seems ok with him as he isn't targeting bigger names.
Whereas at Utd, fans mostly saw the BS under each manager, and the board realized that they arent getting a good ROI on the money they've put in. In addition to that, most managers except maybe LVG, completely lost the dressing room as well