And if it were only that, it would still be a gain. Why get fatter when kebab works? As far as I remember, the engines that need thicker oils are also these that are rather broken. I can think of bmw m engines that can't do 100000 even with the thickest w60 oils. Feel free to ask at every taxi station how many Toyotas already have several 100000 miles on it, you will be amazed. If you don't keep up with the times, you go with the times. We also no longer have the 80s in tribology, but apparently some just stop there...
Most performance engines spec heavier oil guy.
Ford spec'd 5W-20 and 5W-50 for the same engine in the same car, the difference being the 5W-50 spec'd vehicle was the "track pack" version that came with an oil cooler and less conservative ECM programming for thermal protection, while the 5W-20 version would get neutered when oil temperature hit a certain point.
Plenty of high mileage S62 bimmer M engines out there, one guy on M5board has something like 400,000 miles on his now, original rod bearings, runs M1 0W-40 in it.
The bigger concern is that you seem to be either oblivious to, or intentionally ignoring the difference between a performance-geared engine and one sold to power an appliance. Let me know the last time someone sustained 300+km/h in a DD'd Corolla.
My Jeep SRT spec's 0W-40 and my wife's truck spec's 5W-20, both engine share the same architecture, but one's marketed and sold with the premise it's going to have the holy hell driven out of it, the other isn't. Same reason GM doesn't spec 0W-20 for the Corvette.