“eBay Inc. is an American Internet company that manages eBay.com, an online auction and shopping website in which people and businesses buy and sell a broad variety of goods and services worldwide. A majority of the sales take place through a set-time auction format, but subsequent methods include a substantial segment of listings in the “Buy It Now” category. In addition to its original U.S. website, eBay has established localized websites in thirty other countries. eBay Inc. also owns PayPal, Skype, StubHub, Kijiji, and other businesses.”
From Wikipedia http://en.wikipedia.org/wiki/EBay
During the years eBay has become one of the biggest companies for trading in the world. By serving as the middleman in numerous transactions and providing a variety of solutions for trading it had grown to monsters dimensions.
eBay.com was not the first site that offered these services nor was it the first to offer the complete trading solution that it is offering today. There were and still are many sites, similar to eBay.com, that offer a variety of different services.
Check them out on Similar sites to ebay
So what makes eBay the number 1 trading platform? Well I guess that luck had something to do with it and that the tipping point happened for them while it did not happen for many of the eBay like sites.
Today there is no question about it, the quantity of people using it and the full trading services it gives to its user make eBay the number one trading platform.