People are glossing over the fact that using the app to print out a fake id is actually illegal. It doesn't matter whether you could use it to get on a plane or whether you could fool someone used to looking at IDs. It's illegal to use and that is enough reason for Apple to pull it. (And it's not like being unable to use this joke app is a great loss).
I do sometimes think Apple draws the line in the wrong place for some apps, but drawing the line at illegal apps (or DWI checkpoint apps) seems a good place to draw it.
Photoshop is also much more expensive, is complicated to learn how to use, and doesn't come with a database of state driver's license designs.