I will emphasize: because people are paying that much for it. Willingly.

The competition is at Amazon, where I can buy a box of Cheerios, delivered, for $1.99. Or at Walmart where I can buy name brand cereal for $5, and Walmart equivalents for $1.97.

This is a misunderstanding. There is no reason for SOME cereal to not be $8. Competition will not make ALL substitutable products go to the lowest price. The question is whether all cereal is there, or at least all plausibly substitutable cereal is there. And it's not. Someone else did the research, even if you want brand name Cheerios, there is still a lot of range in prices. Unfortunately many people are not THAT price driven, clearly.

Now, all these grocery store do have something in common. They are all in California (if we pick that state), so they all share the high cost of real estate, the high cost of custom formula gas, the high taxes, etc, etc, etc.

And the fire truck example, it correct, is much more of a problem. It's not hard to manufacture breakfast cereals (and clearly not THAT hard to distribute them) or to bring potatoes to restaurants! It's much harder to build reliable fire trucks.