I have not bought a car tyre since about 1995 as the car does not stay long enough but some have still been on the car at 35,000 miles.
Old Triumph 650s generally wear the tyres out at 4000 miles to the point they need changing as they have a flat centre area. Never worn out a front as i change the fronts at about 9 years and very little wear.
I can understand the R111 rear wearing at 6000 miles as it has 2.3 litres of power and 750lb weight. Tyre is 240 width but the centre flats itself