It's because the usefulness of a mouse/keyboard scales exponentially with user facing complexity.
A Logitech MX Master 3 for example is packed with features a user figures out and improves their day to day. Ditto a mechanical keyboard, and generally speaking those work best when the user chooses the particular one they prefer best and learns how to use all the features. Ditto deskmats and all the other desktop paraphernalia that modern desk workers are figuring out is pretty neat.
This is the complete antithesis of everything Apple prides itself on being good at.
Which is a focus on "just plug it in and it works, Apple knows best" technology solutions. Devices which just work when you're using 10% of your brain.
Apple as a company utterly despises user customization in general.
But discrete physical user interfaces like mice and keyboards (unlike trackpads, which operate fine out of the box), is a problem space where user customization greatly improves performance.