the main idea behind the blockade is that Facebook implementing ActivityPub can easily overwhelm any instance small enough in infrastructure through the sheer amount of traffic that such connection would have on the rest of the Fediverse (case and point, the occasional waves of Twitter users moving to Mastodon), and with fewer instances it can get easier for the company to take advantage of that to take over the network and make it monopolized again.

edit: i didn’t read your comment properly, i thought that was lacking context. sorry x.x

edit 2: https://lemmy.ca/post/11771031 someone else shared this thread, it’s an interesting and important read