Culturally, it is much easier to block an annoying person and delete a poorly written post on facebook than ban him on Less Wrong. As a general rule, people like being kings in their own small kingdoms instead of being merely citizens in a larger country, that's why people move to personal blogs. On Less Wrong you are a citizen, you cannot set your rules and impose them onto others and expect that others will simply agree to them.

How would you make that look like a better idea from Eliezer's point of view?

He prefers his Facebook audience. It's a more constructive environment, and there are people whose opinions he cares more about (I assume, he may have other reasons).

We could also stalk Eliezer on FB and repost his interesting comments on LW. Preferably asking his permission first.