They added iOS-esque stuff a long time ago in Lion/Mavericks like “App Nap” and “automatic termination” so it kinda has this, but it’s inconsistent.

Isn’t this ignoring that inactive apps essentially get paged out of memory anyway?

Also conversely what about iPadOS where you can multi task on just 8GB too.

People have survived on 8GB Mac’s for a long time. I’m not sure things are as dire as you make them out to be.

They are both built upon Darwin, Apple's BSD-based kernel, they are essentially the same OS underneath with different top level API's and even those are getting more uniform with Swift and SwiftUI.