It's really a preference thing. I have the opposite feeling, i.e. why keep OS X when you can run Arch?

As for battery life, Linux can very greatly depending on settings and distro. Don't expect to beat Mac OS without any configuration/tweaking, but if you go far enough you can get match it or do better.

Someone that thinks like me! I'm not alone!

Agreed with you, totally off topic, but I spend most of my days doing web development. I opted for OSX over Linux because I wanted to run Photoshop (Gimp sucks), native Word/Excel (LibreOffice sucks), etc. and got tired of constantly rebooting to Windows to export an image in Photoshop.

As I said in the first post, "why not MacOS" is not the question right now. Please, stick to the topic.

Well, it kind of is a question, since I asked it as I would like to know why people do it. Feel free to ignore it though, there's plenty of other comments more on topic for you.

My work (and hobbies) involve lots of linux specific programming. Most of the things (but not all) can be done on MacOS, but almost always linux is the better tool for me, getting my work done. Developing blindly on MacOS, not knowing whether (and how) will it run on linux can't be as good as developing on EXACTLY the same OS that will later run the production version. Using exactly the same (to the exact version) diagnostics tools as on the production server is a thing that I prefer. Especially having seen bugs that only show up on specific versions of the platforms.

Sorry if my previous comment was rude. Didn't mean to.

Thanks a lot for the answer, it makes sense. And don't worry,no offence taken ;-)

Why not use virtualization?

Running native gives increased battery life and makes multiple-monitor support generally easier.