I can't see how it would be country-specific. How else would you have any control of the forward motion of the vehicle otherwise, especially when starting on an uphill slope? You're meant to raise the clutch to the biting point and apply some accelerator and release the handbrake when you are confident that the engine will prevent the car from moving backwards. Taking the foot off the brake and hoping you can move it over to the accelerator quickly enough doesn't give you that control. Drifting backwards into the car behind you when setting off is rather an embarrassing thing to do.

It does appear to be a UK thing. This is from the UK Highway Code. I'm not finding a US equivalent.

  114 You MUST NOT use any lights in a way which would dazzle or cause discomfort to other road users, including pedestrians, cyclists and horse riders use front or rear fog lights unless visibility is seriously reduced. You MUST switch them off when visibility improves to avoid dazzling other road users (see Rule 226).

  In stationary queues of traffic, drivers should apply the parking brake and, once the following traffic has stopped, take their foot off the footbrake to deactivate the vehicle brake lights. This will minimise glare to road users behind until the traffic moves again.

How else would you have any control of the forward motion of the vehicle otherwise, especially when starting on an uphill slope?

By learning to drive a manual? Pardon the snark, but that technique should be reserved for severely steep hills, otherwise heel-toe or just be quick on the pedals. I live in the Seattle area, where you either learn to drive a manual on hills, or you get a punch card from the transmission shop for clutch replacements. Even someplace like going up the hill from 1st and Madison (picking a random, extremely hilly intersection in Seattle), I'll roll back maybe six inches. I'm nothing special, my wife does the same thing. And if you live around Seattle and you sit six inches off someone's rear bumper on a hill, that's a "you" problem when they roll back on you.

> How else would you have any control of the forward motion of the vehicle otherwise, especially when starting on an uphill slope?

That only applies for manual/stick shift vehicles. Most of the US drives automatic transmissions, and you don't have to use the hand brake to start on an uphill slope with an automatic transmission.

I would wager that most modern cars that have a clutch (which is <2% of the market in the U.S.) have hill assist.

Certainly when I've been stopped on a hill with someone directly on my bumper I've used the hand brake, but that's vanishingly rare for me (probably because I live in a very flat part of the country).

Depends on the car. Most ICE automatics will creep forward, EVs will sit there until you hit the accelerator, manual ICE cars (especially diesels) can be held on the clutch just under the 'biting point' which will stop the vehicle moving backwards.