Because on larger amounts paypal takes a rather large chunk out of the money you send to the seller.PLUS as TWINFOGGERSBC has proven, it makes it much easier for a crooked buyer to rip off a seller. example claiming item never arived or wasn't as described etc...Paypal almost ALWAYS sides with the buyer when there is a problem. JUST MY OPINION.
I use ebay and have never sold anything on racing junk but that is my observation.