And a single setting for someone to change now if they want cua-mode.

My point was that making the default cua-mode won't lead to a significant number of new long-term users, so it isn't worth the hassle it would create for people who are already using it.

Also, emacs is not struggling to stay relevant. I fully expect that it will appeal to an audience of users similar to the one it appeals to today for decades to come.