Some do. It's become a popular addition to a middle class kitchen. All offices have them.
As to why Asian households have it and we don't, I think it's simply that we have been boiling water in kettles since the stoves ran on coal, and the electric kettle is just an upgrade of that same old system
Not to mention the age of our housing stock. The Asian households you refer to, when were their homes built? I'm guessing much more recently, comparatively speaking.
Why is the age of the housing stock relevant here? An Japanese-style water boiler is an add-on kitchen appliance, like the Instapot or an air-fryer, so,
cultural differences aside, you'd expect similar adoption rates. Given that we haven't, there must be some cultural component as to why.
Some people have instant boiling water taps with tanks, they're not unknown but rare and becoming increasingly less so. I think this is because a) they're relatively new here and b) last time I looked they cost about £1k plus fitting.
The Japanese water boilers look like they cost £200ish (vs £15 for a kettle) and are bulkier than a kettle. They will save practically no time - kettles boil fast here and while they're boiling it gives you time to put the tea in and any other preparations.
It just occurred to me that Japan also uses 120V (actually I think they use 100V), so it may be just a matter of speed. You can boil water a lot quicker with your 240V outlets than we can with our 100-120V.
You're not taking the amps into account. Voltage without the amps on the circuit breaker is pretty useless. Quickly Googling indicates that a standard residential circuit breaker in Japan is 30A (3000 watt max), meaning you'd get more power than you would in the US with 120v / 15A (1800 watt max), and much less than where I live in Germany with 230v / 16A (3680 watt max).
>You're not taking the amps into account. Voltage without the amps on the circuit breaker is pretty useless. Quickly Googling indicates that a standard residential circuit breaker in Japan is 30A
Sorry, that's wrong. The breakers on my 100V outlets here in Tokyo are 15A IIRC (I'm not home at the moment). 30A sounds like an air conditioning circuit. 30A on a regular outlet would require huge wires; they're not going to wire a whole apartment with that stuff.
I actually have a kettle here, bought in Japan. It's rated at 900W. It's OK for boiling a single cup of water, but it's definitely not quick. Faster than the microwave though: microwaves here are 500W or 600W (frequently selectable), and the high-end ones go up to 900W. All this should tell you something about the amp capacity of the kitchen outlets here.
900W is how much my kettle is rated for, which means it actually draws 900W of power (which is about 9A at 100V).
For the microwave, 900W is the power transmitted to the food, not the power drawn from the outlet. All microwaves are rated this way. But microwaves are not particularly efficient; just guessing, I'd guess that a typical 1200W American microwave draws around 1500-1600W, and certainly no more than 1800W since that's the max the outlet can provide. So my microwave at the 900W setting probably draws a bare minimum of 1100W (11A at 100V).
And that's a fancy microwave; the typical microwaves here are all 500/600W. I think the most powerful one I've ever seen in a store was 1000W, so that's probably the highest power rating that can safely run on typical kitchen circuits here in reasonably modern buildings.
Age matters because in many cases the house was built with some expectations, and something else won't work at all. In the 1950s your house got a total of 4 circuits, which was enough for clocks and lights, one fridge, and a kitchen mixer (an electric range was an option and added circuits). Of course TVs arrived in the 1950s (they existed before then but were not common) and started blowing power budgets. As people started using more electric new houses got upgraded to handle those loads, but many older houses have not been updated as it is expensive (major remodel as you need to tear down walls).
Of course the above is standard, not everyone takes the standard. However it is unusual to take something else.
Builders (read electric codes) build for what is common uses. If everyone wants an something that uses a lot of power the wires will be made to handle that in new houses. However if you want that same thing in an older house you may discover that the rewiring needed makes it not worth it and so you look for an alternate.
I'm not sure that's exactly true in this context. At least, I've never been in the house in the UK where the electrics in the kitchen couldn't handle a kettle, and a water boiler for hot drinks isn't likely to use more.
As to why Asian households have it and we don't, I think it's simply that we have been boiling water in kettles since the stoves ran on coal, and the electric kettle is just an upgrade of that same old system
Not to mention the age of our housing stock. The Asian households you refer to, when were their homes built? I'm guessing much more recently, comparatively speaking.