At the beginning of a project, not much is truly known about the ins and outs of the scope of work, what things will cost, and how long the project will be. Yes, it is predictive, but it's tough to predict everything at this point. That is why high-level requirements are made and agreed upon, and why all projects are progressively elaborated on. Progressive elaboration is a fancy term for go with what you know today and expand on that knowledge once you have it. Elaborate progressively on scope, time, and cost as well as risk, quality, and resources.
For example, we are planning to build a bridge over the Delaware River between Pennsylvania and New Jersey. Predictive means we know we are building a bridge, we know where it will be built, and we know how long the last bridge took and what it cost (maybe). When we are finished, we will have...