Another reason they probably have the debit card restriction is due to the fact that the fees on debit card transactions are much cheaper than credit card processing fees.
I thought that was only true when processed over the debit network? That is, when using pin transacations. In my experience debit cards processed over Visa or MC network have identical fees to the merchant.
On the money-sender side, debit cards have far fewer consumer protections so will result in fewer successful chargebacks. Whether that had anything to do with it, I have no idea.
On the money-sender side, debit cards have far fewer consumer protections so will result in fewer successful chargebacks. Whether that had anything to do with it, I have no idea.