It's not "just as easy". A maven plugin is necessarily a maven module, a first-class module like any of your libraries; unless you go out of your way to make it not, it has versioning, tagging and the like. Even more importantly, since the plugin itself is built with maven, it naturally has dependencies and unit tests, arranged in the same familiar structure as the rest of your code. Everything guides you towards good development practice; of course you could manage your scripts in the same way, but you'd have to do so by hand, and with the best of intentions I've never seen any team that used scripts have the discipline to manage them properly.
Good developers can make good things with bad tools and bad developers can make bad things with good tools yes, but even so, tooling and defaults are extremely important.