The government didn't act like that, they followed their rules. From what I gather, they wanted independent evidence and McDonalds gave them brochures and data printed in-house.

If "everyone knows McDonalds sells Big Macs" is a good argument then it shouldn't be hard to find evidence that it indeed is so. It wouldn't have been hard, McDonalds just didn't bother to provide that for some reason.

If a small, young company would try to defend their trademark nobody would believe them even if they printed brochures, menus, and told "yes, we really really really do sell these". There's nothing of substance in such claims. Printing is cheap.