I've been going to gamescom for the past 6 years now, going again this year. I thought it was really weird that they stopped attending Gamescom. When they were there, they easily took up half of the hall they were in. I can understand not wanting to do lcs playoffs there anymore, but you can attend without an esports event and still make a lot of people happy.
Even now that LoL isn't at Gamescom anymore, you still see loads of LoL cosplayers. There are even a lot of people playing LoL at booths that aren't even being hosted by Riot, and there are always loads of people there to watch it. Really hope they decide to come back one year.