Society might care about cost _including externalities_. A truck running on discarded frying oil might offer a lower price and there’s no way to account for the resulting health outcomes. Exceeding capacity lowers unit price and usually doesn’t lead to an accident. Many industries around the world have shown that without functioning enforcement of reasonable rules you immediately get the tragedy of the commons.

I agree. The OP claims that small fleets are cutting costs to extremes that are bad for society, but the OP provides no evidence of it. By evidence, I mean data. Do you have data on this?