Most likely his voice and his writing was very poetic and stirring sometimes they had a way of winding up in perfection unbeknownst to The Listener until after the fact which makes one kind of want to come back and see if it was a trick or to figure out how they did it
His Simplicity and stirring voice had left the music at the Forefront of minimalistic feeling outside of the Blues format it has the ability to transcend and encapsulate a lot of feelings contrived by people who aren't really sure how they feel at all which makes it very unique in my opinion. It's amazing that the music itself is simple and its structure but somehow it manages to create deep thought
Lou Reed will go down as one of the most influential musicians of all time, and it is easy to see why. His lyrics pushed the boundaries and exposed its listeners to themes uncommon for the time. His influence to the music world is wide spread, and that many artists cite him and the Velvet Underground as an influence. Lou Reed definitely deserves to be ranked among the best.
Since we have no way of peering into the future, it is impossible to determine whether Lou Reed is the greatest musician of 'all time'.
Furthermore there has been no attempt to explain exactly what criteria must be met to become the 'greatest musician'. The question really does not pose a question, but merely indicates someone's feelings toward that musician.