I think Paulo is more of a long stride kind of guy. Like a distant runner vs. a sprinter. He's so tall that when he hits on in the gap, he can glide, but I bet it's harder on him for a short sprint. 
Paulo has been between a 20-30 steal guy for his minor league years 
he attempted more steals in the minors, but his success rate wasn't that great. if you assume that the mlb pitchers are more difficult to run on, it makes sense that he'd run less here.
re. the long strides thing, that may be, but my first guess is just that he's not that good at reading the pitchers or getting jumps or whatever. rios, for example looks pretty slow (and is 90% legs, obviously), but he seems to have real good success. so he probably gets really good jumps.