Why GNU License?

[obvio171]

@codinghorror

We give fantastic forum software to you for free, and in return, you contribute any cool stuff you did with it back to the project so it gets better

This isn’t true for software that runs on a server, right? The GPL only forces you to give the source to users who are actually running your software. So I guess Discourse being GPL might force people running publicly-accessible modified instances to give back contributions to the JS code at best (it runs on the user’s machine), but not the server code. That would require AGPL. Is the JS part the original reasoning behind choosing GPL? Because otherwise it’s basically the same as choosing an MIT license.