The issue is protection. Ebay offers buyer protection, SBF does not. On Ebay the seller needs to provide confirmation that the item was received, typically via tracking numbers uploaded to Ebay either when shipping was purchased thru Ebay or uploaded by the seller. If the item cannot be proven to be delivered Ebay refunds the buyer & is reimbursed by the seller through Paypal (usually why seller funds are held until sellers have an established record). The opposite is also true. If a buyer claims to not have received the item but tracking numbers confirm its delivery the seller has no obligation to the buyer anymore as the transaction is considered complete.
Additionally Ebay offers "item not as described" protection (which SBF does not). If the item is not as was stated in the item description it is possible to obtain a refund, even if the seller makes the item a "no return" item.
These are all Paypal benefits when purchasing Ebay items. I do not accept other forms of payment on Ebay as they do not offer the same level of protection.
I am familiar with their rules and regulations intimately as I have been a top-rated seller on eBay for 15 years with over 6000 positive feedback.
SBF does not offer these protections so trust is earned here, as it is with the real world. I have shipped bats out first many times & paid before receiving many times. I have also offered to ship to a trusted third party member here on SBF.
Read into this how you will but Rusty is correct.