Then you don't have a standard build, you have a build with multiple steps that needs to be documented and/or scripted. In an organization where every other project builds in a single step with "mvn package", and people can check out a repo and fire up their IDE and stuff just works, people are going to get bent out of shape because from their perspective, things aren't working out of the box.

A slightly more powerful build tool that supports custom code in the build doesn't force users to script around it. You can create an arbitrarily customized build that builds with the same commands as a Hello World project. (It's a double-edged sword, to be sure, because people don't try as hard to avoid customization as they would with Maven.)

You can, but why should you need to? Why can't the build tool take the plugin code directly off of disk, build it, and use it? This kind of orchestration of manual steps is what build tools are meant to be good at