I had a quick look through Dreamwidth's "latest" page (https://www.dreamwidth.org/latest) earlier today, and a major portion of the posts on there were blatant spam for things like credit card scams, "Work from home and make $1000/day!", and so on.
You seem to be hosting a lot of spam, and those spam posts are also far more likely to be getting linked externally on sites like Facebook, since that's the reason they're being created.
Because Dreamwidth is effectively free website hosting along with a free new subdomain for each account, blocking individual subdomains is futile, and it's difficult for external sites to distinguish between spam and legitimate blogs.
I'm sure Facebook will unblock you fairly soon, but unless you get the spam on Dreamwidth under control, this will probably happen fairly often with different sites blocking it. It would be easy to end up with an impression of Dreamwidth being a spam-hosting site, and decide to block it (either manually or automatically).
Blogspot has always been in a similar situation and would get blocked from a lot of sites due to the sheer amount of spam it hosts.