The way I see it is that other cruise lines are stepping up their games with reasonable/more affordable pricing while Disney keep raising their price to the point that many families who used to be able to sail with them are getting outpriced.
Also, they only have four ships and Dream/Fantasy are pretty similar and Wonder/Magic are pretty similar. For us, the feeling of "repetition" is already being felt. The new ships are not going to be here for another five and seven years. And the prices for the same "old" ships keep going up.
There will always be a crowd who likes to pay expensive rates just because they can.
And there are people who are more frugal who like having more bang for their buck (value, like beauty, is in the eye of the beholder) that will simply find their happiness somewhere else. My husband is one of them. He's obsessed with Carnival since we sailed with them and doesn't want to sail with
DCL after our upcoming DCL cruise. He found value in a more affordable cruise line and he's excited about RCCL and Norwegian and wants to try them.