Jazz is about soloing. Except, what happens when every one  of the musicians in a group is making up every sound? 

It turns out that there is a simple system that allows everyone to have guidelines for the sounds they can choose.  Using that, everyone can play and even communicate in real time using music!

Music theory is the foundation to being able to not only play what you hear in your head, but also communicate that idea to other musicians efficiently.

Music theory also makes it a much easier to read sheet music as well as chord charts, which is a marketable skill.