Because it's an open and decentralized protocol in the same vein as email. It is the most likely to survive in the longterm as it's not tied to a single entity.

Fragmentation is inevitable in a decentralized protocol. Look at email or http servers, there is no standard mainstream app but a standard extensible protocol, that's how the internet was originally designed to grow. Now that corporations are pushing their own protocols, they have an incentive to lock users in their ecosystem.