[baldfat]

There is a reason, but the audience is the one who choices it's popularity and for what reason they personally use it.

Twitch.tv is exactly this BUT they show the screen and a webcam of the person. You can see both the face and screen of a person. Mostly this is used for people streaming games but others use it while they program and talk to people how they are coding. Others use it for podcasting.

These apps can answer a need, but so often we can't tell the future of what sticks with a group of people. That is why the company that is doing Meerkat is planning to create many apps and fail often to find the app that fits a need that they don't know about currently.