Or they could be trying to light a fire under a series that's lagging behind by turning it over to an author that moves more books?
Why would they? They let DS9-R go into hiatus as well. There's no rule that says the TV-descended series have to go on.
While there have been no books titled Deep Space Nine
in a while, the characters are still a key part of the 24th century books.
There's really no where to go with the Enterprise
characters if there are no books. If those books are underperforming then you have to take a look at why and what can be done to fix them. Changing authors seems a good place to start since the last several books have been written by either Andy Mangels and Mike Martin or Mike Martin solo.