I think in most European cities, alleyways that are too narrow for cars have either been ‘improved’ and widened or demolished or they have been made footways where motor vehicles are not allowed. So in Europe, where many of us map, there isn’t much need for a tag that means “street too narrow for a car”, and that is probably why it’s taken 20 years for someone to propose it.
But OSM is a project with a global scope. Narrow alleys where motorcycles are allowed are not just common in Asia, but also in some North African cities (e.g. the medina of Marrakesh). If a mapper from one of those regions says they’re missing a tag for them, we should listen…