Earlier quoted context omitted.
Trademarks are a red herring here. What the GPL says is that if Automattic attempts to get someone to give up their GPL rights (e.g. the right to fork) , then Automattic automatically loses their own GPL rights as punishment for the attempt. This is the section 4 you speak of. Specifically, Automattic cannot offer terms that say "in exchange for trademark stuff (or anything else), you agree to give up your GPL rights…
I really don't think that's the way to interpret it. Automattic is saying "you have the right to fork, but you can't use the trademarks if you do". The GPL says that's allowed -- you're not required to grant a trademark license.
The contract says the opposite – it states "you can use the trademark, but you have to forfeit your right to fork if you do"
Such an attempt to get someone to forfeit their GPL right-to-fork (even for consideration) is forbidden by the GPL license granted to Automattic, and the punishment for violating that GPL license in such a way, is that Automattic forfeits their own license.
Automattic is not allowed to propose a contract which limits someone's GPL right-to-fork. They did so anyways, and thus should lose their own license.