I don’t know much about federation issues with programming.dev, but I think the reason why there’s so many results from that instance is they’ve changed how active users are calculated for their communities. Instead of it being just users who post and comment, it’s now users who post, comment or vote on anything.

I saw a post about it yesterday (in their Meta community I think), and wondered how it would affect these lists. I’ll have to see what it’s like in the coming days (that instance will seem way more active than every other instance, but each community’s activity growth should stabilise, hopefully)