Yam vs Sweet Potoes = it's whole thing
Ube is a purple yam from the Philippines that is used is many different recipes, especially desserts. Sweet potatoes are pretty popular in Japan, as well as many Asian countries (most of the world though TBH). I DID find it interesting that OP mentioned his wife being Japanese and adding Ube, as I said before, it's usually associated with Philippines. BUT there is the Purple sweet potato (I grew up calling it Okinawan Sweet Potatoes). For more light reading: https://themamareport.com/exploring-the-sweet-tastes-of-ube-and-okinawan-sweet-potatoes/
As far as popularity... I think a lot of Asian things are gaining popularity as a whole. With KPop and JPop, anime, tiktok, skincare, etc, things get out and go "viral"
That Neiman Marcus chain letter... talk about a relic!