It doesn't matter what I am. The point is that twitter doesn't monetize properly right now and the primary reason for that is that people don't consume the content twitter links to on twitter but somewhere else.

I don't know what the primary reason is.

Facebook has directed huge amounts of traffic to external sites for years and that doesn't seem to have been a major problem.

You consume way more content ON Facebook than you are aware of. Thats the big difference. And a lot of content is being written ON FB. The discussion is ON FB and they allow them to be long which keeps people there too.

Just the ability to do a preview of on article is such a big eyeball keeper that it leaves twitter in the dust. Or to write a comment to the article which make people then react to what someone wrote about the article without maybe even reading it.

It's like with checkins. People think FourSquare and Swarm is big but it's dwarfed by FBs checkins it's just not a major focus for them and so we don't think about it as a place a lot of people check in. But it's a numbers game.