Many people don't understand what they're talking about. Those restrictions you talk about are purely to stop copyright reattaching itself in the future.

Anyone who uses copyleft really wants to declare the following: "This is not copyrighted and derived works shall never be copyrighted." That is not possible with current copyright law. Copyleft is the only way to get that.

GPL is not about enforcing restrictions, it's about doing what's necessary to neutralise the damaging effects of copyright. The fact that is uses copyright to achieve that makes it one of the greatest hacks of all time.