Do Data Scientists prefer MACS?
This question is highly subjective, like asking what colour keyboard is best for programming faster.

A large number of Computer Science research at universities is done using Unix based operating systems (normally a Linux variant like Ubuntu) because it is completely open source and allows the user to tweak things as they please. Windows never allowed this officially. Apple's OSX doesn't either. However, OSX is based on Unix like Linux, and so there are many more similarities in every day usage between Linux and OSX than Linux and Windows. Many of the poster-boys/girls from data science have an academic background, where they likely used Linux.

Because many of the latest research ideas come from universities (where I claim most researchers use Linux), it is common to see open-source projects that have only been tested and packaged for Linux usage. Making them run on OSX is a smaller jump than going for Windows, as OSX and Linux are more alike.

Other guesses as to why many pick Apple products, are that they generally have higher build quality, they have a reputation for many thing just working (though IMO, Microsoft and Linux have become almost as good in that respect) and they are marketed as being luxury consumer products - and so are visually appealing. I'm sure there are books written on how social psychology with respect to this. All this ends up with the price being somewhat inflated for the actual hardware parts that you get.

In the end, someone who wants to get work done and has the necessary skills  will manage it on a 10 year old netbook running Windows. Likewise, owning a Linux server with 8 GPUs and a Macbook Pro to remotely connect to that server is no guarantee of good work. I for one have worked on all three platforms, for data science as well as other tasks, and although I have my preferences, the operating system rarely poses the biggest problem.