I answered a question on Quora:
I can think of a number of reasons:
A 2x2 is a nicer way to present options than a slide with 4 bullet points, a 5 dimensional space can get very complicated
It forces you to think things through thoroughly for holes and overlaps, maybe you start with 2 options, add a third, take a step back and think what actually defines these 3 options, come up with the 2 axis, and then realise you overlooked option number 4 to be complete
A 2 dimensional framework allows you to think about what happens if you move things around, and makes it easy to visualise.
In most cases there are more than 2 dimensions to a problem, but it is hard to visualise (see point 1), and think about. The 2x2 forces you to choose the 2 most important dimensions.
Cultural habit, if you are in a place that uses a lot of 2x2s, you will use it more often, it is a language that people understand easily.
SlideMagic has lots and lots of 2x2, 3x3 and other matrices as slide templates for your to get started. Download the app and get started.