Why only have the link to bitcoin core at the top, and not classic, unlimited and XT as well?
It's easy to remain the client used by most users if you control the main platform of communication, but this is not decentralized at all.
Bitcoin Knots (
https://bitcoinknots.org) for example is listed on Bitcoin.org while others aren't because XT , classic ,unlimited etc... do changes to the network rules which makes them an Altcoin , as simple as that.