The short answer is alignment of incentives.

The longer answer is that, although Amazon does provide many tools, as I'm sure anyone who has attempted to use them for cost analysis and/or forecasting has found, they are, at best, difficult (i.e. require a remarkable amount of human labor to extract the desired information, if that's even possible). At worst, one discovers that it's impossible to find out what one truly wants from the tool, even after exerting the effort, although it might be a close approximation. Amazon has little incentive to spend money improving a tool that would help their customers send them less revenue.