One of the reasons I never bought a license was the cost. I followed a Unity course over two months and wanted to develop mobile games. I had the skill to, but committing $400 to something I'd never really done before was insane.

The Apple developer license, Corona/Gamesalad, etc. are far more affordable and less risky. I'm not even sure if you had access to the iOS/Android API without purchasing a license, so I guess you wouldn't be able to practice it.