I find it astonishing that what is basically a short message broadcast service can generate billions of dollars of revenue.
Basically a short message service? That's naive. Twitter is a marketing platform with 300m people signed up to receive marketing materials, people who also readily provide the platform with the details of what they like/would likely click on/spend money on, where they are in the world, what age they are, what gender they are and more. Of course it's extremely valuable.