You quoted Smith Chapter X Part II, whose argument in context is that the pressure of competition quickly kills attempts at collusion, while surviving conspiracies are enabled by regulation.

The paper contrasts commodities from all other concentrated markets; whereas the former is expected to have an impulse transient response whose price discovery quickly settles by way of competitive forces consistent with Smith, the latter has a salient capacity as price maker to play games.

Megacorps and multi-nationals weren't exactly meta in the 18th century. Exponential tech complexity, sector consolidation, global economies of scale, regulatory capture, the speed of information and capacity of market participants to meaningfully act are just a few modern barriers to entry in concentrated markets suppressing the notional competition that Smith leans heavily into.