I honestly think that part of the reason is simply that a sizeable percentage of Glaswegians are just miserable bastards
I sat for years in my ST in CR2 and we had numerous miserable cants around us who just seem to be at the game to vent their load and spew out abuse every single week.
I genuinely used to spend significant amount of time speculating just how shite their lives must be that it produces that amount of pent up frustration
I eventually gave up trying to get singing started and get those around me to support the team. It was pointless. Only games in europe or v the various forms of tims and the sheep ever produced a decent atmosphere