Make is very optimal at the stage it is, everything above or below it it's just not that optimal.
Right: GNU Make is at a local optimum for describing how to generate products based on rules and a dependency graph. I'd also wager it's close to a global optimum.
GNU Make is certainly closer to that global optimum than Boost's jam or the countless homegrown XML-based things I've seen over the years --- make is powerful, but despite that power, simple things look simple and are simple to write. In other systems, either simple things are hard to write or the system itself is so simple than it's not powerful enough to describe what I want done.
It has its hear in the right place, though. High-level build systems should strive to be as declarative as possible. It's the rest of the design which is problematic :)