In your opinion, why buy a mac instead using Linux?
I wonder what are the advantages of Mac versus Linux

At this point I wouldn't. But it's simple: want a solid device that needs no high effort maintenance or deep domain specific knowledge, but want UNIX and commercial support. Mac's will run much of the useful open source UNIX compatible software as well as Adobe software, and you're more likely to get supported by hardware vendors. No fiddling with drivers, Linux kernel versions or settings, switching between DEs, etc. Less flexibility, but less brain cycles wasted on things you may not care about.

@jchw thank you! It's a great answer !

My only reason for having a mac is iOS development. As soon as I can do iOS dev on Linux I will no longer use macOS.

Here are some reasons people are into Macs:

1. You have to. You are developing for MacOS and iOS software like Ryan says.

2. You really like using MacOS, whether it is the stability of "it just works", a polished user experience, or it simply looks good to you.

3. You can't live without some Apple only software such as Sketch, OmniGraffle, Logic, iMovie, etc.

There are none. Simple as that.

@jchw I agree with most you say. Especially commercial support. Most important things on Windows also have Mac support. The driver and kernel version fiddling is wrong. Especially when you take a bit care selecting your machine. Last time I had to up the kernel version was 7 years ago to support a brand new raid controller that was not in the stable version (e.g. 4 year old kernel) of the storage OS.

OS-X:
Install time = 0
Lots of app support
Lots of comercial support
Works great with all your other Apple stuff
Don't have to look for Open source alternatives for your fave program (this can be a major point)

Linux:
Better hardware for your buck
Faster and easier to maintain your development platform/tools
Something's are Linux specific and your development setup is a bit closer to production
Works better with others (Apple lost my respect when they failed to work with vanilla SMB actively ruining standards)
More customization options if you are willing to take the time.

Because ooh, shiny (that's part of the reason I switched anyway)

None