Agree, but it is as popular as it is because they have some of the best marketing. I've never understood it's appeal but I think it's all about the cachet of being seen with the distinctive green bottle in your hand.
Mind you, not all of their beer is knat's piss. They bought a Swiss brewery in Chur which produces and distributes the KP for the Swiss market. Said brewery's original product Calanda is a very good lager.
But what irks me is that Heineken will sign exclusive deals with restaurants and bistros where the proprietor gets special prices if they agree only to sell the KP. They can't even carry Calanda if they sign these deals. Bar-stewards, literally.