It's just their mark-up.
However, for certain things, it's worth it to have them act as the quality screener for a product, because they send you a good item, and have to deal with sending the defective ones back to India.
You wouldn't believe the absolutely worthless defective shit that some of these India vendors will ship to you. On the streets in India, thete is a thriving industry of knock-off parts. Maybe some good, but a lot of bad. Nothing is wasted there. They try to find somebody to stick with the junk, no matter how bad it is. A lot of that ends up on Ebay.
You can get good stuff on Ebay too. It's a "crap-shoot", though. If you have to send a heavy item back because it was defective, the return shipping costs you more than the item is worth. So then you are stuck with it and you can't blame the vendor because he says he'll replace the bad item if you return the bad one. That's how it works.
With duckbills, it might be worth the risk because they are cheap and the shipping is light weight and not very high. Probably a good idea to order a quantity if they are that cheap, because it will raise the chances that there will be some good ones in there. Oh, and saying "Genuine Royal Enfield Spares" generally means that they had the printer down the street print up bags or stickers that are copies of RE bags.
So , this happens to NField gear too. They "buffer" you from the defects, and pick the good ones out of the mess, and if they pass thru a bad one, you can return it cheaply and easily to them for replacement. They take the losses or the hassle on the load of crap that remains.