Maven is generally considered by many to be a build tool. Many people who come to Maven initially are familiar with Ant so it's a natural association but Maven is not just a build tool, and not just a replacement for Ant. Maven is an entirely different creature from Ant. Ant is simply a toolbox whereas Maven is about the application of patterns in order to achieve an infrastructure which displays the characteristics of visibility, reusability, maintainability, and comprehensibility.
Without these characteristics it is highly improbable that multiple individuals will work productively together on a project. Without visibility it is unlikely an individual will know what another has accomplished and as such there is a very good chance useful code will not be reused. When code is not reused it is very hard to create a maintainable system. When everyone is constantly rooting around trying to figure out where all these different bits and pieces are that make up your project there is very little chance anyone is going to comprehend the project as a whole. As a result you end up with the silo effect, a decay of shared knowledge along with the commensurate degree of frustration among team members. A natural effect when processes don't work in the same way for everyone.
Maven was born of the very practical desire to make several projects at Apache work in the same way. So that developers could freely move between these projects, knowing clearly how they all worked by understanding how one of them worked. If a developer spent time understanding how one project built it was intended that they would not have to go through this process again when they moved on to the next project. The same idea extends to testing, generating documentation, generating metrics and reports, testing and deploying. All projects share enough of the same characteristics, an understanding of which Maven tries to harness in its general approach to project management. On a very high level all projects need to be built, tested, packaged, documented and deployed. Of course there is infinite variation in each of the above mentioned steps, but this variation still occurs within the confines of a well defined path and it is this path that Maven attempts to present to everyone in a clear way. The easiest way to make a path clear is to provide people with a set of patterns that can be shared by anyone involved in a project.