As a Twitter non-user I don't get it either. But hey, the results don't lie.
The way I see it Twitter is either a broadcast channel for people who want to share lots of self-important things or a stalking channel where people can follow celebrities etc. Eithe way I don't see people buying stuff unless it is celebrity endorsed.
And it can be more targeted than something like Facebook because they can say "Show this ad to people who follow our competitors" (I have no idea if you can actually do this in the platform now, but I'm sure they are working on something like it). That is very powerful because those people presumably are in your market and since they follow your competitors they are welcome to seeing ad-like tweets in their timeline.
You can do exactly this on Facebook, and it is very effective. Twitter's ad platform is better built than Facebook, but targeting will likely always be better on Facebook because it simply has more information about users.
Also FB ads are so much more invasive. I am not the average user though.
Overall, the amount of targeting you can do on Facebook dwarfs Twitter, regardless of how atypical a user you are.