Postmates earned 400% more on a delivery than the delivery guy

I used Postmates to buy and deliver a $199 Chromebook for me from Best Buy. The delivery fee was $5, 80% of which went to the delivery guy. Postmates added a 10% "purchase fee" which they do NOT split with the delivery guy. So they made $21 while the guy who actually did the work made $4 (not counting the tip I gave him).

I realize that developing the app that facilitated this transaction is work but for the purposes of a single transaction is it truly 400% as much work?

Does anyone else have a problem with this?

Receipt image: http://goo.gl/z4HBdv