The way they write excites your brain. In a nutshell:
It is Shakespeare’s inventions–particularly his deliberate syntactic errors like changing the part of speech of a word–that excite us, rather than confuse us.
See This is Your Brain on Shakespeare | How to Think Like Shakespeare at Big Think for more on what great writers do to your brain.
P.S. Anyone looking to excite people with their writing or presentation material would do well to read this. We are not Shakespeare, yet we can tweak the brains of others if we try.