Some folks with expensive college degrees, who are a whole lot smarter than me, in the past have explained:
OEMs often calibrate WOT over rich to prolong the life of emissions equipment such as catalytic converters.

It's not done for the sole purpose of killing power. It's done to save car companies money
because in the United States there is a Government mandated 8 year/80,000 mile warranty on emissions equipment.

I guess there is a chance I was being lied to, but it seems to make sense.

https://www.epa.gov/transportation-...ent-questions-related-transportation-air