I'm not saying a microwave is better or not to get an electric kettle. I'm just saying folks never seem to even consider a microwave. In the US it is more likely that a microwave is present than an electric kettle and it is much easier to use than a stove top kettle (unless maybe you have an induction stove).

I think another part of it is that in the US hot tea is often seen as a more quaint sort of ritualistic thing than hot coffee is. Yeah, some folks like to do fancy pour over coffee but it's rare. I think stove top kettles just feel more whimsical than a microwave. I think many US hot tea drinkers would view someone saying "why don't you use a microwave" the same way an audiophile listening to vinyl might react to someone asking why don't they just use Bluetooth with Spotify. That's all fine and good, I don't see a problem with it, but even apart from those folks people just never seem to even realize they can use a microwave to heat water.