Who is the test audience for Disney movies? Kids, adults, both?
If it's primarily kids, I can see how the garbage continues as I don't think they really care about plotlines. If it has funny characters doing funny stuff, I'm sure they are fine with it. The fact that adults keep taking their kids to this stuff, says more about the state of parenting than anything else. Stop throwing your money at stupid movies to entertain your kids.
Also, I think Hollywood in general (Not just Disney) has completely run out of ideas, and this is only going to get worse as time goes on. Hence, the amount of remakes, sequels decades after the original, , etc...