With all the hype it received im not surprised, besides FFXIII-2 is the worst selling FF to date, at least in the first week in japan only sold around 500,000 copies that shows that people got so dissapointed with XIII that most were reluctant to get the sequel.
FF is dying, luckily i dont care for FF anymore, with series like Growlanser, Persona and of course Suikoden, the rpg side is covered
Sequels to and remakes of numbered games have never, ever sold as well as new numbered games. Final Fantasy XV will likely outsell XIII regardless of how people felt about the latter. Hell, people were predicting Final Fantasy was dead after XII was so divisive, then XIII went on to outsell it by a landslide.
Also: Growlanser and Suikoden are fairly dead/dying series at this point. The former is only being ported and re-released (much like Ys) and the latter has done all it can to shed its hardcore fans of the past 4 years.
Growlanser WoT for psp is more than just a port, i have played the original for PS2 and i can safely say that the PSP version is a completely new game, it has around 50% more content than the original. As for Suikoden im new to this series, i have only played S5 and now i plan to finish all the ps1 and ps2 games.
FXV will outsell FFXIII because fans hope that SE will wake up and remember how to make a proper FF title wich i higly doubt it happen, Suikoden for psp can still come (At least i hope).