Dear Op, America is not the only country in the world, did you know that?
FFXIII is considered the best Final Fantasy game in Japan, followed by X, followed by VII (Yes, this is why FFX is getting a remake, not VII, because believe it or not, America isn't the only damn country in the world, nor is it the country they are in, nor is it where they make their most damn profits!)
Square makes their money primarily from Japan, their biggest player base is in Japan, their biggest place to sell IS JAPAN. It makes me mad as hell when Americans are like, "Y U MAKE THIS, EVERYONE LIKES THIS", no, they don't, Americans like that, Japan likes the one they're remaking most. Seriously, let me ask you, Is Final Fantasy VII considered the best game of all time in the west? No, it's not, in Japan, FFXIII is literally the best game of all time in Japan. Source, Famitsu issue 1104 where fans voted Final Fantasy XIII as the best game of all time.
Next thing coming up, FFXIV was ill received because it was riddled with bugs, not because it was a bad game, it was an unplayable game, they're fixing that for the upcoming PS3 version, it should be good, and it was ALWAYS planned for there to be a PS3 version, from the start, I know, I was planning to get it, but it got delayed because of all the bugs.
Next up, the guy who is making Final Fantasy Verses XIII has been caught up in the Kingdom Hearts fanaticism, Final Fantasy Verses XIII was his next proposed project and was announced until Kingdom Hearts mania swept the gaming world and he had to go off to appeal to them for a while. At the moment, Final Fantasy Verses XIII is having full development time devoted to it, it is being focused on as a top priority, so stop spewing forth fallacies.
To reiterate, they're not considered the worst in the series, they're considered the best, just because America doesn't like it, doesn't mean the world doesn't.