On MacOS, you still get local user accounts and Apple's optional online features are still optional.

Microsoft is using all the levers at their disposal to force users to use online Microsoft accounts to log onto their local computer and even turn on formerly optional features like One Drive.

My assumption is that Microsoft is using their access to user data to build up everyone's advertising profile, and forcing you to be logged on through a Microsoft account makes sure that the data they collect is linked to a specific person.

Windows Recall is another example of a "feature" they wanted to force on users that can be used to fill out everyone's advertising profile.

Why is your assumption for Microsoft different from Apple?

If Microsoft was worried about serving the needs of end users, wouldn't they offer free customer service like Apple does?

Apple's main revenue is not from advertising but mostly from expensive hardware

It is not ok on iOS or macOS or even Android or whatever else. The feature to have some online storage with backup is fine, IMO, but what is not fine is the OS nagging you to use that feature. This thing must be opt-in and only if the user themselves initiate it.

Also it should not be locked to a single online storage provider but use some sort of standardized protocol (or at least some pluggable mechanism) to allow any online storage provider - including using self-hosted options - to work with it.

This is how you make something that works for your users instead of taking advantage of them.

Does iOS constantly (multiple times a day) spam you if you don't enable backup?

(I've had it turned on for so long that I honestly don't know what they do.)

I’ve never enabled iCloud backups and it has never pestered me about it after the initial iPhone setup process (the modern version of which doesn't even pester me then since it copies the setting from my last iPhone). I backup locally to my mac, which admittedly they made require a password each time now, which is a bit annoying, but it’s not asking me to enable icloud backups regardless.

They have always required a password for encrypted backups, do they now require for all local backups? Or is unencrypted not an option anymore?

Yes, it periodically pesters me with it.

you sort of, answered your own question. the lack of user value for microsoft is a keystone.

https://en.wikipedia.org/wiki/Keystone_(architecture)

Err... I don't understand what keystone means in your sentence.

Frankly it's more of a fact than an occasionally seen odd double standard behavior at this point. It's literally not okay when Microsoft does it; iPhone users literally love this exact same feature. They should be working a lot harder on solving this mystery.