[OJFord]

Why's that a problem?

Surely a kettle (ahem) boils down to a simple resistor (the heating element) that gets good and hot, boiling the water. P=VI, so if you halve the voltage (wrt the UK) you need to sink twice the current. I=V/R, so if you need to double the current (and voltage is fixed) you need to halve the resistance.

Is the problem that they're rare enough that they're all import kettles safe at 110 but designed for higher voltages?

[mastax]

The maximum current you can draw is based on the ratings of the plugs, cabling, fuses, circuit breakers, etc. Regular US appliances use less than 15A. I believe UK is similar at about 13A. The voltage available almost doubles the available power.

[OJFord]

Yes, and a kettle is a likely candidate for the cause of a trip, but (in normal operation) the vast majority aren't near that, a little over half.

AmazonBasics kettle (first result for searching kettle) for example is rated 1.5kW.

I'm just sceptical that all American kettles can suck, and mains voltage be the cause. If that were the only reason, and otherwise you'd all love them, you'd have a 'kettle socket' on higher amperage, as for ovens (here too, 32A).