It’s unclear that’s the case, because there are other limitations at work! Merging is a huge time cost and slows down two lanes; the more lanes, the more merges are necessary to use the new lanes. There’s some work suggesting it makes more than three lanes in one direction essentially useless in urban areas - and that’s where the traffic is…
I mean it in the literal sense, past a certain point the city no longer exists as the lanes replace all other land uses and by definition without any source of traffic, the traffic will cease to exist as well.