The shipping services are listed by the seller, not ebay. If a seller has option A for $9, option B for $20, and option C for $35 for shipping options, the seller lists whichever options he/she would like to use. If he/she only wants to use option C, then you would have to pay for option C. If the seller wants to be nice and give you 3 options, then you (the buyer) can choose.
Put yourself in the seller's shoes for a second.. Yeah shipping a parcel for $6 sounds great. You don't get a tracking number or any insurance, but hey, it's $6! The buyer will be so happy! A week goes by, now two weeks. The buyer never got the package. But that's okay, the buyer only paid $6 so that's okay right? No, now you're out the $6 for shipping and the cost of the item. The seller needs to cover their end as well.