Well, they just want to be successful doing what's popular at the moment. Sometimes you have to keep up with new trends for success. I don't think it's always a bad thing.
I don't think they try to imitate what the younger artists are doing, it's like you said, following the trend.
Older artists also need to grow their fanbase and can't rely on their once young fans, so the only thing they can do is, do what's popular and get the sales.
Nothing wrong with it, just depends on how hard they try to follow the trend, sometimes they can go over the top.
I understand staying relevant, of course. But like any art form, I personally believe that drawing upon personal inspiration provides a fount of unbridled creativity for truly visionary artists.
Then again, this is mainstream pop we are talking about. Enjoyable yes, but hardly known for originality.