The reasons you probably don't understand could be down to the manager / landlord being under pressure to sell some of the overpriced beer and other rubbish kindly supplied by "the brewery". Just another of Maggie's attacks on the working class, making sure all her mates got into the pub trade cheap to make immoral profits.

If people sit all night with half a pint / bring their own soft drinks and even booze / leave a mess of rubbish they can't be bothered to be sensible with then eventually the axe falls.

The Old Hat Band were kicked out of pub in Whitby for not drinking enough but that might be considered a special case as they were taking up a whole (large) room and were not actually official guests of the festival that year. It was also late lunchtime in a pub that sold quite a lot of good food.