Yes, hotels do charge more than postage for returning left items. It does take time on the part of hotel staff to organize and ship the items back. The hotel certainly should be compensated for the time/effort.

However, I've noticed that a lot of hotels use outsourced providers to ship items back. In these cases, the fees are much higher than postage + handling alone.

In either situation, you get reunited with your left item, so there's value in that.