Many monopolies form by first using a dominant market position to sell at a price no competitor can afford to match. Choice has already been removed before the “competition” folds or pulls out of the market. The consequences don’t happen overnight; you feel the squeeze before the “true” monopoly emerges. Amazon isn’t going to sell at a cheaper price once their competitors go out of business out of the kindness of their hearts.

Further, high consumer price is just one form monopoly power takes. Reduced labor power, wages, and worse working conditions are other important concerns, in addition to removing product variety and innovation incentive.