It's not "theirs", they have only been granted a limited-time monopoly on it in order to incentivize the initial creation. If they abuse that monopoly, we (i.e. society) CAN take it away.
If only... Copyright monopolists lobbied governments to the point they extended the duration of that monopoly to multiple lifetimes. About 5 years of copyright protection is more than enough for creators to make their money back and then some but for some reason these people saw the need for it to last centuries. Copyright is functionally infinite, we'll all probably die before the works we enjoyed enter the public domain.
In effect, we've all been robbed of our public domain rights. The social contract was: we'll all pretend the creator's works are scarce for a while so they can make money, and then it will enter the public domain. These monopolists aren't really keeping up their end of the bargain so why should we keep ours? The second we stop pretending, they're done.