One very practical reason that comes to mind is waterproofing. Kitchen counters get wet, and office desks do not. Anything with a plug is at greater risk of shorting.
I tried to figure out how to buy that exact kettle recently because I typically store mine away in a cupboard (and so a "cordless" kettle with separate base is just an annoyance to me) and couldn't find it anywhere.
I had to settle for a Proctor-Silex branded unit that was only sold by Home Depot online. It does not have a detachable cord.
I'm from the UK (although haven't been there for a decade+) and remember "lead" being used in place of "cable" or "cord" by those around me. Plug would be the other end, which goes into the Mains.
Yeah, I know, I was just giving the colloquial name for them in the UK. We like calling things plugs, including what you might call a socket or outlet. Not exclusively but very commonly.
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.