Windows has a very fine grained permission system. But as you can see, the issue isn't a lack of this system.

Windows pervasive fine grained permissions is better than UNIX, it goes all the way down to OS resources.

The OS isn't to blame when people give root access left and right.

Actually this is why macOS got SIP.

Yes and no. Windows has a very fine grained permissions system, including at the admin level. The problem is that it was designed for multi-user systems in the 90s, so the permission and security systems are mostly concerned about keeping users safe from each other, and having administrator roles for managing those users and doing system-wide tasks. Preventing a process from injecting code into another process by the same user running in the same session just isn't in the original threat model, since it's just the user screwing with their own stuff.

The shift towards protections from malware happened mostly as a consequence of Windows XP. There are now better controls, like assigning low-trust processes like a browser's renderer a low integrity level to prevent them from doing that. But it's also late enough that it's hard to rock the boat too much without breaking existing applications. Microsoft tried to make a clean break and offer more sandboxed applications with a user-friendly package manager (called the Microsoft Store) but this wasn't well received by app developers: most didn't use it at all, and those that did often opted out of the sandboxing.