In order to be able to get information on the web, people need to put it on the web first. And for that to happen, there needs to be something to motivate them to do so. What those motivations are is going to differ between people and situations, could be a pure desire to contribute to the commons, could be part of how they make their income, could be any other number of things. But if putting something on the web means accepting that you're going to be helping vile companies achieve their goals and the way most people may see this information is in a perverse form, riddled with falsehoods and with no attribution (or maybe worse, mostly falsehoods attributed to you), and there's nothing you can do about it, that's going to put a damper on a lot of those motivations, and the ones that aren't tend to be the less desirable ones.

And it's not just information that's on the web, it's also collaborative efforts like open source software. Why do people release source code under licenses like the GPL? Because they believe those constraints lead to a better outcome than if they had just put it in the public domain. That their contributions to the commons lead to more contributions to the commons, even from people who may not be inclined or incentivised to do so. If it becomes trivial to undermine those licenses (and for the record, those licenses do get enforced and there have been companies that had to release the source code of their products because they violated the license), that may undermine the reasons for many to contribute to the project.

You can be all cool and cynical about how social contracts are made up and whatnot, but let's be honest here; if someone beats you to a pulp because they didn't like the way you looked at them, you're not going to just coolly accept your broken nose and displaced ribs as just the way things work.