It's that their power is feeble. It's half the voltage of ours. Generally a kettle in the UK is 10 Amps. So at 220-240V that's 2.2-2.4kW. In the US they are apparently 12A, so at 110-120V that is 1.3-1.4kW. Feeble, so takes ages to boil water.
I fear gen Z brits are just watching so much America YouTube & TikTok they think that's how to do it. I really hope I'm wrong.