There’s probably someone who can explain it better than me, but MacOS is a Unix-based operating system that’s been around for decades. iOS was actually built off of it. The reason MacOS looks like a “giant iPhone” these is probably because of iPhone’s popularity and a push to make macOS more approachable to people who are more familiar with the mobile device than computers. Macs are still very capable computers at heart, although they aren’t as straightforward to tinker with as you might have grown to expect after using windows and Linux for do long. You can always watch a YouTube video on MacOS evolution if you’re interested.