I don't understand the appeal in this for the designers either. Back in the old days (~2010s) every UI had some personality and very intricate details that the designer would be proud of and that will differentiate them from the competition. Nowadays it's the same flat, white and empty UIs everywhere - there is no significant difference. Would a designer really be doing their personal brand a favour by putting one of these new "designs" on it?
The appeal is that they need something on-trend to put in their portfolios for career advancement. It's their version of résumé-driven development. Project managers have similar incentives (screenshots are very powerful, in many settings) so at least don't stop them, if not actually encouraging them.