Remix is one of the major react meta framework and is based and focused on react-router. Because the last few years they worked so much in improving react-router (by themselves or in concert with the react team), most of their features got implemented directly and react-router. So much that it makes sense for them to just merge with react router so all the react community could profit from their work. Thanks to the remix team for all their implication, they definitely improved the way we are using react now.