Presumably they pay rent in those malls, and the bigger the store, the more rent they pay. The problem with that arrangement is that you need to be at a certain minimum scale in order to afford rent at all - you can't just occupy a free/basically free store to play around and make toys in. Taking a commission avoids that issue by making 'rent' scale with the amount of business you do, not how much floor space you need.

I'm not saying that 30% is the right amount - I really don't know. But the mall comparison doesn't seem like a cut-and-dry case to me at all.