Star Ocean 4 had absolutely nothing going for it. No word of mouth whatsoever, no marketing, no press coverage, no buzz, a fatigued, overserved market who had just received a flood of RPGs only a few months prior, a heavily competitive release month with several high-profile, eclipsing titles....literally nothing going for it.
Beyond that, you have the fact that Tri-Ace's recent track record is anything but impressive. Star Ocean 3 left a bad taste in many peoples' mouths, the PSP remakes gathered next to no attention, and Infinite Undiscovery released as an extremely poor game that shied a lot of people away from Tri-Ace in general. As a developer brand, Tri-Ace is certainly not going to carry a product anymore.
So what does that leave? The game would have to stand on it's own merits. And, frankly, nothing about Star Ocean 4 really stood out in any meaningful way. It had absolutely no hook that was going to draw attention to itself from what I could tell, and without favorable market circumstances or developer brand power, it desperately needed one.
Of all the things that happened in the February charts, Star Ocean 4 doing poorly is really not surprising at all.
The more interesting topic of discussion, imo, is whether the announcement of PS3 being the official Evolution/tournament version of Street Fighter was the catalyst for higher proportional sales for that version of SF4. If true, it could indicate a much higher interest-level and sales presence of the "SRK crowd" than I would have personally thought to exist....
