If i can buy a part directly from the manufacturer in China for $3.99, I'm not going to pay $11.99 for Amazon to deliver it to me or even $5.99 for an Ebay reseller.
The problem is, last time I wanted to get something through Alibaba, I had to order at least 10 times the amount I needed, or get a sample for 10 times the shipping costs through FedEx (or similar). I checked the shipping costs from china myself and they were correct. This made the transaction not worth it so I just waited 2-3 months for someone to buy in bulk to dilute the shipping cost and to resell in small quantities on eBay
That was 2-3 years ago, but nowadays I see small items with low shipping costs on eBay. I also get daily spam in chinese now about similar items that I inquired 3 years ago, definitely through me trying to do business through Alibaba. For as much as I dislike having to use eBay, it is a much much better experience than Alibaba for the average person.