According to an interview recorded in Pinball Magazine:
Stern was going under in 2009. An investment company headed by Dave Peterson stepped in and rescued it. That company must have had to put a lot of money in, and they now own Stern. They therefore now call the shots.
But it has to be a good thing for us that they did step in - how many great pinballs have Stern produced since then? AC/DC, Metallica, Tron, Star Trek, Walking Dead...
And I'd guess
@stoptap is right, the money men control Stern, they took the gamble rescuing it, and now they want their due profits.
Sadly I think they're in danger of killing the goose that's laying golden eggs. Pinball prices are rising way too fast to be sustained.