Absolutely possible; that's not the problem here. The deeper problem is that Carto gets a free ride on the website as the incumbent house style. You can fork i

Absolutely possible; that's not the problem here. The deeper problem is that Carto gets a free ride on the website as the incumbent house style. You can fork it, but doesn't make it the default style shown on openstreetmap.org. You could fork it, get popular community support, and still get nowhere except for wasting a lot of effort, because displacing Carto takes a lot of political manoeuvring as well as server resources for hosting the default style (which are not insignificant). If it was a matter of just forking it, and have the openstreetmap.org website maintainer pick it up if it proved more popular than that would be that, but given the fact that the one other Carto maintainer who seems semi-active is also a member of the OpenStreetMap operations working group (i.e., server resources), spending any effort on a fork with the goal to displace Carto seems pointless at this point in time. I prefer to spend my resources on just making the map better. Some people justly pick up their crayons and go make a nice thing elsewhere (like the Americana style), or contribute to the styles used by popular apps. For now part of the community just gave up on Carto and is waiting to see how developments for the new vector style will pan out.