It's primarily because I want things to consistently work as expected. Sure, macOS doesn't always work as expected, but compared to my experiences with various Linux distros, it does.

Others have mentioned the trackpad experience, and that's a thing, but not a deal breaker for me since I use the keyboard a lot.

Hardware quality is another issue, more important than the trackpad for me. MacBooks are built like tanks compared to most other laptops, and it's not difficult to keep one running well for 8+ years. In fact, I have a 2013 MacBook Air and a 2015 MacBook Pro, both of which are running as well as ever.