I wonder if it's perhaps because of industry lobbying. The incentive to buy a 400+ BHP BMW M3 (or whatever) would probably be somewhat stymied if it were limite

I wonder if it's perhaps because of industry lobbying. The incentive to buy a 400+ BHP BMW M3 (or whatever) would probably be somewhat stymied if it were limited to a mere 85mph. And there are plenty of way less expensive cars out there with 300+ BHP. Again, not much point if you're limited to 85mph, which means the car industry has one less lever to pull to charge premium prices for premium models, and thus makes less money. And we're talking about an industry that's already, at least in some quarters, struggling. (This could be complete nonsense of course.)