Maven is a build tool (in fact, a build manager) similar to ANT. The main task of any construction tool is to set up a project, compile using the necessary projects and final packaging. The script construct in your project gives a blue print of the project structure. This frees you from any custom dependencies on a particular IDE, such as Eclipse. All you need to know is the standard build command, and you can build your code almost anywhere.
Now, back to your question, why not do it in Eclipse?
For a simple project and a small team, Maven is redundant. You can easily pass on the configuration, IDE to use, and indicate any special steps that need to be taken. Nevertheless, in large projects, there are many dependencies loosely connected with each other. To begin with, various settings will be set for building the developer's machine, assembling tests, and assembling. There are requirements for running automatic tests, integration tests, storing an assembly package (artifact) in a public repository, and updating versions of various modules.
Obviously, if all the steps mentioned above are performed manually, there is a chance to skip the step. In addition, the manual process takes a lot of time.
Ideally, you should choose the tool that suits you best. If you think you can achieve what you need without Maven, it makes sense not to use the Maven / build-tool just because everyone uses it.
It is proposed to study automatic deployment, this will give you a more complete picture of what all the materials you can do with the building tools. And if you don’t feel this adds any value to your current process, you probably don’t need Maven or any other build tool right now.