This is Ebay / PayPal's policy and you're absolutely right, it does not make sense.
IMO, a good seller would pay for the return shipping on an item damaged in shipping or one returned because it didn't match the description. Ebay doesn't force them to, though and in fact makes it harder to do. The seller has to issue the refund, then do a seperate PayPal transaction for the return shipping. The refund can't be more than the original payment. It would be so easy for them to allow this and then charge the refunder the appropriate fee on the overage.