This comment troubled me so I did some reading.

1. You can run Linux applications on elementary. There's nothing forcing anyone to use the store.

2. The split is actually higher than you said for cheaper app apps because the minimum cut for elementary is $0.50.

3. There is a review process which I assume involves human effort.

4. Significantly, there is no enrolment fee and no subscription cost. So you could consider this a referral / hosting fee for elementary.

This seems reasonable actually. Projects need money to run.