Because addressing the widest possible audience isn’t always the way to go. Attempting to address the widest possible audience will surely let some others go, which means you’re never able to address the widest possible audience as you’re always forced to make a choice in this. Imagine if I used 100 words to describe something 50% of my possible audience would get in 1 word to address the 50% that would need the 100 words to get it, woudn’t it be a terribly boring read for the former 50%? If I were to continue that style, I would surely lose their interest, which in turn would make that a barrier. So, a barrier on one side may be a trampoline for the other.