Allow me. When you take you time and research, well the other manga listed there are something that I never heard of nor know that they weren't listed in the top 10 manga selling of this year. So by that, people would be like, "Er......Never heard of them. So I'll choose the one I do know." TG grew tenfold this year, so it out beat Naruto when the sequel is already ongoing. So to me, it's not easy to tell the true opinion of people. It's like I vote for this candidate because well, I really don't know what to choose out of the two and really, don't care for the election. Plus it didn't help that TG is like playing Mortal Kombat after playing Mario.
Ignorance on the part of the readers doesn't mean those series aren't popular in circles beyond your own. There's obviously a reason for these obscured (to us) titles being ranked so highly on a top 10 endings list. And it must have something to do with their favourability, otherwise all of the manga that are ending this year would have an equally valid excuse to get onto that list.