I think the 50k is to make the tires disappear

Yes. A high UTQG rating will mean your tires will last forever at the expense of traction, road noise, etc. The last set of tires I bought at Costco lasted 70k miles, but also increased wet stopping distance and introduced a roar to cabin noise. My latest set have a UTQG near 0 and will only last about 10k miles but they make no noise and have insane amounts of grip (think race car tire)

If you drive less and have separate summer/winter tires, it has the odd side-effect of making long-wear tires not worthwhile, as the life of the tread depth will exceed the life of the rubber due to age.

I drive about 3.5k miles a year, the OEM tires would have given me 70k miles but I would have never got there. the michelin pilot sport 4s where $5 more per tire and would survive just about 7 years (i'm planning 3-4 with the occasional track day). the tradeoff was DEFINITELY worth it, but now i'm deathly afraid of potholes and road hazards lol!

(after 1000 miles on the MP4S you're already more than 1/16th worn and would need to replace the entire set to keep the AWD system happy)

I've done 60k miles (96 kms) on my current Michelin Cross Climate tyres. The front ones are going to need replacing soon; but the rear ones are still good.

That is on a 2008 Toyota Prius so not the lightest of cars.

Somewhere around that, yes. Unleas you kill one by accident before that. Screws and tires don't mix too well...

Good tires driving on mostly paved roads should last at least 120k kms. In the US, you pay $120-200 per tire for those, but they also come with a warranty that will replace them for free if they wear out before the distance advertised.

That's not how treadwear warranties work. They're not "replace them for free"; they're pro-rated, and there are all kinds of restrictions and limitations.

https://www.consumerreports.org/cro/tires/why-tread-life-war...

My mistake, I was thinking of road hazard warranties