Guinness is practically religious cult for some people. Once they've have been brainwashed they won't accept anything else. I used to be a barman in a pub that served Beamish instead, because the manager preferred it, and being a contrarian like myself he refused to give in and switch to Guinness. People would ask for Guinness, then grumble when told there wasn't any and order a lager or a bitter instead, or sometimes just walk away to find another pub.
You get all this nonsense about "the best pint of Guinness in London" when it's the most bland beer produced in a massive factory, where they'll have a laboratory and chemists to make sure every batch tastes exactly the same, and it's all sealed in pressurised kegs. It's a marketing triumph of style over substance, with lavish marketing campaigns and the business of pouring it slowly to give the thick creamy head that rises just above the rim of the glass.
I can well believe the club will sell a lot more Guinness than London Black, and probably have a bigger profit margin per keg, but it's disappointing nonetheless because London Black is a far superior beer in my view.