How come? Because for kent it's a very small venue (1500 people or something) and since they rarely play such small clubs I guess it gets very special. And since they are one of Sweden's biggest bands the tickets always gets sold out. Or maybe your question was just rhetorical, haha. Sorry.
Sadly also, there are evil companies in Sweden that buy a lot of tickets and then sell them for a much higher price. It's not against the law, but it fucking should be. I don't know how many tickets they got their dirty hands on this time though. Perhaps none, which is always good since they promise rare tickets in advance and when they don't get them they get a lot of bad press.