Why changing engine coolant more often than factory recommendation matters

Agree. Which is why I have done ten coolant changes over the years.

 

Then why aren't more cars affected by them?
Corollas especially used the same 2ZR-based engine and there were twice as many of them sold, AND their head gasket failure rates are not even close to those of the 'turd-gen' Priuses.
Same head gasket.
Same coolant.
Same maintenance periodicities.

I completely agree with the FACT that Toyota's "lifetime" fluid change periodicities are only meant to last the 'lifetime' of their OEM warranty period.
It's also true that their coolant will break down over time and can damage gasket material.

 

Thermal cycling of the Prius

 

"I completely agree with the FACT that Toyota's "lifetime" fluid change periodicities are only meant to last the 'lifetime' of their OEM warranty period. It's also true that their coolant will break down over time and can damage gasket material."

There is truth, evidence, and some common sense in that comment

Green coolant used to be flush every 3 years. Red (Dexcool) 5 years - as I recall.
FWIW I would be inclined to 5 years flushes on Priuses.

PS I advocate distilled water instead of potable/ drinkable water to mix the coolant.