Same as a lot of what has been already been written.
(1) I hope to transfer some of the outstanding talent to my competitive teams.
(2) I think it is just a natural progression for some folk, especially after competing against live competition. It's kinda like - been there.... done that and now it's time to come back home.
As you have stated, solitaire is not for everybody. Conversely, some also find-out that live competition is not for everyone.
In my eyes
this appears to be a real comprehensive list that supports the reasons for this "resurgence."
Good questions.