My guess is that they want to be considered Christians for the sake of converts.
It gives then the cloak of respectability to the outside world.
For years being better than and separate from mere “Christians” was a draw. You would never see or hear the word Christian used anywhere in or around the LDS.
Then they went overseas after tapping out the market in the states back in the 70s and 80s.
Overseas they found “Christan” was a great brand name.
Now they are the best “Christians” on the planet.