Why would it be? Grad school is great for learning to be a better researcher, to understand problems better, and to write a bunch of crappy code that nobody else will ever use that you yourself want to never touch again after your paper gets submitted.
In other words, grad school will help a good scientist become a great scientist, but it will not help a good programmer become a great programmer. In other fields the same is true -- it will help a good architect become a great architect, but it will not help a good bricklayer become a great bricklayer.
In other words, grad school will help a good scientist become a great scientist, but it will not help a good programmer become a great programmer. In other fields the same is true -- it will help a good architect become a great architect, but it will not help a good bricklayer become a great bricklayer.