Or maybe... and I know this sounds crazy... it could have gone somewhere that hasn't had one yet at all?
But let's be real here: KupoCon is ultimately a business, not a charity. The reason they keep holding events in the UK is presumably because they keep selling out. The fact that it's an English-speaking country is also relevant (this applies to all KupoCons which have been held or announced so far) and the lead organiser being originally from there might also have something to do with it. He's said many times that the UK fans have been incredibly enthusiastic about the events and I've seen that reflected on their social media as well.
Nevertheless, I am a little surprised that the third UK event will be so soon after the second. I wonder if they'll be in the same "generation" of events, because if so, people going to both can probably expect a fair amount of repetition. Personally, once a year is enough for me, not because the last time wasn't magical, but precisely because it was – I wouldn't want to diminish that by doing it too often. With that said, I'm going to be in the UK anyway next June so if the summer KupoCon lands then, I'll consider it.