John, I know of a couple of reasons, which may not be Mike's.
1) They charge a pretty good fee, whereas a check is nothing.
2) They delay transferring the money to your account, so I think they can make interest on your money.
3) They have a grievance system, which is mostly good, but can be abused by scammers.
4) They are owned by ebay.
I see that this is a bash on "PAYPAL" so I'll put my 2 cents worth into the conversation.
I have had both good and bad experiences with PAYPAL,
but 99.99% GOOD!
A charge? Of course. Does your credit card service give "Free" service? I think not!
A delay? Does your bank hold checks "til they clear"? Mine does....
Who cares who owns them? I sure don't. I care more about Chinese good in this country..............etc., etc., etc.
They are the fastest and best way to pay for goods that I know of AFAIC.
Jerry
PS: Burned? Hell I've been "burned" on this site! It's called "The cost of doing business".