1st, thanks for pointing out that you can *choose* whether to bring over your followers/following list from #Instagram into #Threads. I hate Meta, but I hate inaccurate description more. Now that you know it, I'd appreciate if @h_tejas could edit your post.
About using Insta vs. Facebook database. I guess Insta is a younger user base and can adapt to this microblogging format than Facebook users. And Insta still has a more favorable view than Facebook.