A MacBook is not the same thing as an iPhone. Even the implementation of ProMotion is different:
iPhones in general can go from 10Hz to 120Hz, with 12 distinct refresh rates in between to choose from.
MacBooks are just like iPads and have only 5 steps, plus the lowest is 24Hz instead, so it's far less efficient than an iPhone.
On top of that, the software stack for a MacBook is not always guaranteed to use exactly the recommended frameworks Apple provides to support ProMotion. See here...
Provide custom animated content for ProMotion displays.
developer.apple.com
iPads and iPhones in general benefit from the fact that there aren't Electron apps, Java apps, Qt apps, etc... running alongside apps made using Apple's UIKit, SwiftUI and SpriteKit. So unless you're suggesting everyone using a Mac is running just Safari and Apple-made apps, you have to accept that ProMotion is not really "functional" for many other apps made using other tech stacks. This is a known issue.
You'd think I'm blind and couldn't just check actual display refresh rate on my MacBook Pro 14?