Maybe related to the strong cultural bias against throwing away rice ! My girlfriend always glares at me if I don't finish every grain 😂

I believe this is not a recent change. Kaiseki restaurants with a donabe rice end course have offered to pack up the leftover rice (sometimes they make it into onigiri) for me since the first time I went in 2021, before the recent tourist boom. I've never seen leftovers offered in any other context.