Don’t we want these big platforms to adopt ActivityPub?

I certainly don't. I abandoned Facebook years ago because of how BS they were getting with privacy concerns and social manipulation. Last thing I want is to bring those dumpster fires here. They join the platform, I will migrate to whichever Instances defed them or leave Lemmy entirely if necessary. Simply put, it's been a breathe of rational, civil air here. While it is early days keeping that hostile-to-humanity crap out of here is obvious minimum we should be doing.