Sounds like a legacy thing.

Exactly. UK and European legacy standards required cold water dishwashers; US legacy standards called for hot water dishwashers. Once that expectation took hold, it’s somewhat difficult to alter it. Builders install plumbing for their respective systems; consumers buy appliances to match their plumbing. It’s a vicious circle with little compelling reason to break it. Neither is objectively better; neither is objectively worse.

Though I do think it’s very likely that a big chunk of it is as the other commenter said, an electricity thing.

The overwhelming majority of households had gas-fired water heaters, because for decades, it was significantly cheaper than electric, and those gas-fired systems remain in place in a majority of homes. In that sense, it’s an electric thing.

In the sense that US circuits simply can’t handle the current requirements of a permanently installed heating appliance, that is a complete myth. Trust me, we know how to waste use electricity.