US electrical is weird.

We have 240v mains in basically every house (a very small percentage have 480v, which is normally reserved only for industrial buildings).

However, that 240v gets split at our local transformers into two 120v phases, separated by 180° phase. This allows either 120 or 240v (120+120) in our homes.

So yeah, most plugs including those in our kitchens are 120v.

However! A 120v electric kettle still blows out any other heating method, especially gas, gas is soooo slow. Some high-power induction stoves can keep up, because they can dump boatloads of power into a kettle and are really efficient, and honestly even small induction hobs like mine aren't much slower (5 mins instead of 3). But an electric kettle is like $25 and uses less power. They're so useful!

Only slightly longer than a 240v kettle, but still much faster than a kettle over a gas range.

Real reason is that most people in the US don't drink tea and don't have a need for quick hot water on demand.

I've heard that too...of course, I can't compare to 240V but it takes me probably 2-3 minutes to boil about 2 cups of water and probably 5-6 for a full kettle at a rolling boil (rough estimate from memory). It's not much faster than the stove but theres no wasted heat, and no hot pan sitting on a burner after I'm done. Another theory I've heard is that in the US people opt for a drip coffee maker instead of a kettle (for their one spot on the counter? Why not both?), since we don't drink tea that often.

I don't think they're that uncommon in the US. They're not ubiquitous like they are in Europe but I feel like the majority of people have them. As mentioned, it's probably more to do with whether you drink tea than anything else, and not as many people drink tea all the time here. Come to think of it, I've never seen anyone boil water for tea on the stove in the last decade. They either use a kettle or they don't drink tea at all.