Because the title of the site then and so my old bookmark reads "Crypto-Currency Market Capitalizations | Bitcoin Litecoin Peercoin Namecoin Novacoin Primecoin Feathercoin WorldCoin CryptogenicBullion Devcoin and more..." when I set the bookmark in around 2013. Only two, Bitcoin and Litecoin are still widely talked about, the rest has more or less gone into oblivion.
I just thought I'll mention it.
The reason why those coins are already being left behind on the the top list is because they have not sustained the sales and movement of their coins. It is the developers fault for not making a good marketing to uplift their coins. Also to mention they are not the only coins being washed out of coinmarket.cap there are also coins and hundreds of them that are being left behind and died without a value.