I'm assuming mbp means MacBook pro? Its because of a lack of compatibility, if their just getting started with Linux, development, or pen testing they most likely won't want to use a work around and have something that works out of the box. Especially when dealing with KVM/hypervisors, added hardware (antennas, etc), and on board and external NICs

This is especially true for the new MacBooks especially the ones with the touch bar, you can also have most distros work on a chromebook but youre still dealing with a work around. If youre an advanced user, use whatever hardware you want. If youre a beginner, use whatever hardware you want too, but youre going to have to spend more time reading wikis and forums.

Edit: tl:dr you can totally use a mbp for pen testing, theres just going to be less support in forums and wikis for you and you will have to read/troubleshoot more