I don't know about that. X-2 had a lot of hype and effectively sold pretty well. I'd say it's because XIII disappointed and X didn't, generally. It just sounds like X-2 was something people were okay with, and XIII-2 (in contrast to a newly developed FF title/world) was not asked for. Glad to hear this one sounds like it's a bit better than the original, though.
i remember FF12-RW on DS got a lot of hype and sold well too
this title lives on the bad impression ff13 left to the mainstream audience