Sure but that's what gfci is for no?

Anyway IMO lamps are usually the worst offenders.

Not every house has GFCI, and old ones are not always retrofitted.

From top of my head, there are two main reasons:

1. C13/C14 is a bulky set of connectors, and fitting them to compact(er) things are not always easy. This also means cable needs additional care to keep somewhere else and label. Why label? See 2.

2. Not all appliances use the same amount of power. C13/C14 is an overkill for a small, non-grounded appliance. Use a figure 8 then, alright, but what happens when you mix your coffee grinder cable with your powerful hand blender's cable and use it at max power? Hot things. Not the soup, but burning cables.

In this age where we use aluminum cables because it's cheap, mixing low and high power appliances' cables will become a liability fast. Using unique connectors will make the reason to have detachable cables moot, and drive up the price.

Standardization? The awesome thing about standardization is, three are too many standards to choose from.