EDIT: This is meant to be educational, not a rant. I'm hoping people take it that way.
Maven requires a standard directory layout. Maven chose that hierarchy, because:
1) Namespacing. With tens or hundreds of thousands of packages out there, there needs to be an unambiguous way to refer to them separately.
2) Multiple language support. Maven can do Java, Scala, Clojure, Groovy, and so on - in the same project, even. It can even do Javascript, which isn't a JVM language, in certain cases. For the JVM languages, if you want a multi-lamguage project, there has to be an easy way to interoperate (this is enabled by namespacing).
3) Separation of test code and program code. Don't ship tests with your binary package.
4) Separation of code from data.
5) Automation - of packaging, IDE support, etc. This has to do with all of the previous ones. You want to produce a JAR, but don't want to include the default log configuration. So you package the project up. It just happens. You want to edit the code in your IDE. So you add the project. All libraries are downloaded and on your classpath. Add a few lines to your config (as a per-system-user setting or per-project setting, take your pick). Java documentation and source code for those libraries is automatically downloaded. Eclipse hooks it up for you.
Suddenly, this:
src/main/java
src/main/scala
src/main/resources
src/test/java
src/test/scala
src/test/resources
...makes a lot more sense. It's hardly overengineering, but even then, the engineer isn't the one engineering the build system; these are details Maven takes care of.
[Aside: I am appalled and flabbergasted by the ignorance typically leveled at Java by people who don't understand it✝. It has real flaws, don't get me wrong, but making dependency resolution and installation ridiculously straightforward, multi-language builds dead simple, and unit testing a core feature - these are good things.]
Take a look at ant and compare it to maven and you'll see which one makes your life easier✝✝.
✝ I have worn many hats, and have experience with Python, Ruby, PHP, C, Java, and a little bit of Scala in real world contexts, among others. So I'm not a noob who hasn't experienced elegance or conciseness or performance. Java is actually an amazing language that many people don't give it credit for. Though the syntax can be pretty ugly even when the code is conceptually solid.
✝✝ Losing a bit of nuance here - ant gives you configuration. maven gives you convention. Ant is good for very custom; maven is good for straightforward processes.