The BMI is a tool, and with all tools, it's succes depends on it's application.
The BMI is a global assesment of someones position on the bodyfat scale and the associated risks.
It's a tool that can be used on the majority of the population and in that respect it's a quick and useful method.
Some situations require a closer look and a different tool than the BMI, with bodybuilders that's case. In most cases it's the fault of the applicant using the wrong application/tool, not the tool itself that is to blame.