Cuthbert added in a follow-up tweet, "because Monsters is such a good fit it is being pirated I think," and then he responded to a suggestion to incorporate anti-piracy measures into the game code with: "unfortunately the pirates could just hack those kinds of things out." While the PSP Go has yet to be fully unlocked by would-be pirates and download-only PSN titles seem to be well protected from piracy, PJMD is available on UMD (in Japan and the greater Asia region), which has no doubt lead to the distribution of pirated versions of the game.
While it's somewhat naive of Q-Games to not have anticipated a piracy issue, it's no less disheartening. The PSP has long suffered from a lack of consistent third-party support because of a history of sales losses due to piracy. Q-Games is just the latest developer hesitant to commit further resources to supporting the PSP platform, and without the release of an impossibility firm firmware, it won't be the last.
Update: Cuthbert reemphasizes that PJMD sales will be the key determining factor that drives Q-Games' future in PSP development. Cuthbert's studio has not definitely dropped PSP development, but ostensibly low sales over the first three weeks of PJMD availability have Q-Games in some doubt about pursuing further PSP projects. Of course, a sales spike could certainly change that attitude.
[Via Examiner; thanks, Marcus N.]