A few years ago Zenimax received a large investment to acquire talent. I think it was $150 million or something. When you have a board of directors that include Jerry Bruckheimer and Donald Trump's brother as well as the original investors who want Zenimax to "acquire talent", then you're going to have members asking why Zenimax isn't making money outside of their core Bethesda studio (Scrolls and Fallout).
Since Zenimax botched Demon's Forge with inXile and Brink with Splash Damage, they had to bank on Arkane's Dishonored and Human Head's Prey 2. Arkane is what is today because of Bethesda. Dishonored is a success because of its original creators. Prey 2 is a strange IP though, since it was Bethesda's only sequel at the time and previously owned by the Radar Group. Doom 4 has had its own issues. Wolfenstein wasn't even known about when Prey 2 started having whatever happened to it.
Both Doom 4 and Wolfenstein's rights were purchased along with iD Software. There's no reverting of ownership after no use.
Prey 2 on the other hand could revert back to the Radar Group if it's not used by a certain time or declared cancelled.
It could be Zenimax realized they were caught with their hand in the cookie jar with Human Head from a legal standpoint and it created some sort of stalemate. Zenimax's CEO is Robert Altman who was previously a lawyer
http://en.wikipedia.org/wiki/Robert_A._Altman. Maybe there's some period of time they were waiting out to legally do something else with Prey 2. Or they just couldn't find a developer with the talent or time to do something with Prey 2 until now, since they obviously didn't want to work with Human Head anymore.