It must be a regional thing. Arizona has many landscape practices that are strange to me. (I lived in
Scottsdale when I lived in Arizona and could not believe the horrid tree and shrub pruning I saw there by landscape companies. Probably ignorance of these companies.)
The overall performance of perennial ryegrass is lower than fine turf- type tall fescue and Kentucky bluegrass throughout the United States. If you are the Phoenix area, you'll read water conservation departments discourage overseeding because it uses so much water. Overseeding any cool season grass on warm season causes immense stress to the warm season grass, just when it is attempting to store nutrients for the winter. Tourism drives overseeding in your area. I understand that.