People are just used to kWh. There's nothing about it that's more intuitive, it's just more familiar. But measuring things in hogsheads and barleycorns used to be familiar too. Sometimes being familiar isn't as important as following standards. Eventually the standard units will become familiar, and since they're standard units, they're much easier to work with.

not actually understand how power usage of watts of appliances would convert into Joule energy units

1 joule per watt each second. It's dead easy. That's why Joules should be used.

That’s why electric cars motor powers are still rated in Watts

Yes, power should be measured in Watts, that's the standard unit for power, just like Joules are the standard unit for energy.

To add to that, that’s why so many metric countries (not USA) still use imperial units colloquially because they are more relatable in real life like

No they're not, it's just that people are used to them. The people whose minds are the hardest to change are the old people who have used some random unit for all their lives and don't want to have to get used to some newfangled standard (a standard that's actually hundreds of years old at this point). Because the old people refuse to change, the country gets stuck using that old unit, even if it's informally, and so that's what the kids learn, then they become old people and are also inflexible.

There's nothing about an inch or a pound that's naturally more intuitive than a centimetre or a kilogram. It's just what you're used to. Go somewhere where people grew up with metric and for them using anything other than metric feels strange and awkward. Pilots and sailors are used to knots, they never had to switch, but when they do complex calculations they mostly avoid using knots because doing conversions with non-SI units is such a massive pain in the ass.

What makes lbs, inch and feet more relatable?

How is half a kg more relatable than one kg? Or how are 2½ cm more relatable than 1 cm? Or how are 30 cm more relatable than 10 cm or 100 cm?

I keep seeing your argument here and there, but I just cannot fathom what is meant by it. For me there's nothing relatable at all in "foot". It falls awkwardly between 10 cm and 100 cm and I cannot really make heads or tails about it. Except if I divide it by three, which gives me an approximate number in metres. But then the number could have been in metres in the first place.

Sorry you totally lost me on the second paragraph. What you describe there is basically a British thing. On the continent people use m, kg and such for daily life things.

Knots are used because of historic influences and inertia. Imperial units in some special cases are exclusively used because of the influence of the US and again inertia.

So weird phenomenon actually, because our military is fully metricated, you wind up with some of the most die hard American exceptionalist/American nationalist types fully using metric and 24 hour time. A friend was raised in a household like that where they just didn't use US customary at home because the military doesn't.

We're all taught a lot of the basics in school. And yeah we have an instinctive idea of what 2L looks like. Drug users know grams, as do some bakers (a lot of baking is still done by volume here). And other than that I'd say maybe a quarter of Americans know that a meter is kinda close to a yard. Maybe 5% (may be overestimating tbh) know that a liter of water is a kilogram.

Slowly but surely though more things are being roundish numbers in metric here (like 325 mL/12.9 fluid ounces) and I think that's a vital component of the move to metric. We are actually headed there, we're just slower than the UK and Canada.