Actually, I would suggest that quite a few play mallets including Kuchar, Adam Scott, Duffner and others...

However, I would agree that blade style putters are most popular probably because of the feel and feedback they offer...

IMHO

I believe it is because it offers the most control and feel with a traditional design. You also have to remember that they are playing on greens where the stimpmeter is through the roof.  So the need for complete confidence and control in my eyes is the traditional flat stick. Many pros used the blade style when they were growing up and like Jordan Spieth, it what he used growing up. He uses the exact same one and it definitely works for him, so why change. This being said, there are still plenty of players that have mallet putters on the tour. Above anything else, "it's the indian not the arrow." Hope this helps! 

I have two Newport 2s and love the feel.  Nothing truer and the tale of the indian.  Well said Craig.  

I have a Scotty Newport 2 and also a Scotty Golo 3.  I find that it is much easier for me to line up putts of all lengths with the Golo.  I'm sure it's all a matter of personal preference, though.