The immediate suspicion is that Namco has exerted pressure over TMA to halt distribution of the offending title.
A terse and uninformative announcement is all they offer by way of explanation:
“Due to various circumstances, release has been cancelled. We sincerely apologise for any inconvenience caused, this is truly inexcusable.”
All mention of the title has been removed from their site, though for the time being it still remains in vendor databases (such as Amazon). It is not clear whether there is any chance of eventual release, as they offer no dates and the language used is ambiguous.
Adult Master was due January 16th – we can reasonably suspect that it has already been completed and production is finished, so the possible obstacles to its release cannot be numerous.
In lieu of any other explanation, it seems legal pressure or similar from Namco, the owner of the Idol Master rights, is the most likely cause; the sudden and unexplained withdrawal of a completed product on the verge of release seems unlikely to have any other plausible explanation.
This could make Namco the first such pornographically defamed rights holder to have any success stopping the distribution of cosplay parody porn; even the likes of Nintendo and Koei have previously been unable or unwilling (unlikely) to stop them.
A case of the copyright/trademark holder exercising legitimate control over their rights to prevent the release of a product damaging to their reputation, or chilling legal harassment likely to threaten the creation of other derivative works, such as adult doujinshi?
Doujinshi at least are non-commercial and widely tolerated, so we might think them relatively safe…
TMA’s more obnoxious works have included celebrity parody AVs (including one of Aya Hirano) as well as the usual slew of titles very closely resembling the official products, so it seems likely they are hated by subjects of their pornographic “parody” – we might wonder if this is not the beginning of the end for them, as those tired of their antics strike back…