#1 Far too close to their independent name
WWE likes it when their superstars make a fresh start once they come on board and join the WWE system. More often than not, a lot of independent stars have to leave their former gimmicks behind. I mean look at Finn Balor. He is not Prince Devitt anymore during his WWE stint.
The War Raiders AKA The Viking Experience was formerly known as War Machine. They were a highly decorated Tag Team in the independent circuit and even won gold in other notable promotions like Ring of Honor and NJPW.
I am not certain that this is the reason but at the same time, it is all too possible that this could be one of the causes for the recent name change. WWE probably wants them to erase every trace of their independent wrestling past.
Like it or not, you're stuck with The Viking Experience.