Part of the problem is technical, part of it is social.
The social part is that a lot of webmasters just don't think about it: they don't give their scripts any license and often don't provide the source code either.
The technical part is there is no easy way to tell automatically if any program is free. This isn't a problem for most programs because a human needs to manage the repo of a GNU/Linux distro or a catalog of free software, but for Javascript, there are just so many scripts, and they are frequently used transparently.
So yeah, NoScript is definitely not the best solution, and LibreJS doesn't really do much better (the only improvement is that it gives is helping you actually look at the Javascript files, but even that is not very useful because LibreJS doesn't let you choose specifically what scripts to execute; your override is either all or nothing).
Actually, come to think of it, why didn't LibreJS just fork NoScript, take away the other security features it has, and add the license and script triviality detection and change the default whitelist? Then it would have all the stuff NoScript has, including not introducing errors into pages, plus extra.
