I'm trying to think who on Earth would even have that many things to plug in on a kitchen counter.

Microwave, toaster, toaster oven, rice cooker, griddle, blender, George Foreman grill, coffee maker... you'd run out of counter space well before you run out of outlets with that scheme.

I have relatively few outlets, (House was built in 1968) and I don't see the point either - you keep everything unplugged until you have to use it. I typically keep the rice cooker, crockpot, and all of the other "occasional use" appliances in the cupboard anyway. The only appliances that I actually have in a fixed spot are the microwave, toaster, and blender. Three outlets in three different spots, no problem.

That's what I am thinking while looking at my seemingly cramped kitchen with by comparison massive 24 inch deep countertops with only 4 outlets (5 if you count the one hidden behind the refrigerator). Much more than 18 inches apart. It boggles my mind to have that many outlets.

The motivation is keeping people from being dangerously cheap.

Quite a few kitchen appliances draw 12A for long periods of time, and people love to get cheap extension cords and outlet strips that cannot handle that amount of load. These same people will plug multiple high power loads into the extension cord, making the cord get dangerously hot before the breaker trips.

Just having extra outlets though would not help with that much if more than 1 or 2 appliances were drawing that much load and did not have their own breaker. The standard 15-20 amp breaker powering all or most of the copious outlets can still be overdrawn if the occupant plugs in too much kitchen stuff. It is my understanding that usually the refrigerator has its own breaker, but the rest of the appliances are on a common circuit.

Edit to add - just checked my breaker box. It looks like the disposal and the dish washer each have a 20 amp breaker and the rest of the kitchen is on a 3rd 20 amp breaker, presumably along with the refrigerator. It's an old house though, CA code is probably pretty strict on the breakers.

Having multiple outlets on the same breaker is fine as the house wiring will work fine with the trip current of the breaker, and it even might get inspected during installation to make sure it was sized correctly (this varies highly by location and the amount of change/new construction).

The cheap non-fused extension cord someone is using for both their microwave and toaster oven typically cannot safely handle the over current until the breaker trips like the house wiring can.

These 18" receptacles are not on one, or two circuits, wired in parallel. Now, if every receptacle was required to be isolated, your explanation would make sense.

Use to be a union 6 member. The code might now call for every receptacle to have it's own circuit breaker. It wouldn't surprise me.

Lobbying from the outlet lobby, most likely.