One reason eBay is a good place to sell is that the company is very protective of buyers.
When buyers know they can safely send their money halfway around the world and get what they paid for, they come back and back and back.
But that buyer security comes at a price. EBay charges hefty fees to let sellers into their venue.
Like Amazon they charge a fee on shipping too. This has the side effect of making sketchey sellers, who used to cheat on fees by charging low asking prices and skyhigh shipping straighten out-- or go to some other, less secure, site.
And the limit on selling for new sellers? Again, buyer protection. An eBay seller cannot list 5000 items, take the money and ship nothing. First because he can't list that many items, and second because Paypal, a subsidiary of eBay that also operates on other sites, will not release the buyer's payment for 21 days after it clears, allowing time for the item to arrive be inspected and good feedback to be left.
Buyer Protection.
(But yeah, it is annoying for honest new sellers to be lumped in with the scammers.)