But why gnu? They seem like a static site that can only be taken down by simple ddos?

The Emacs web server had to garbage collect.

https://www.emacswiki.org/emacs/HttpServer

Everyone has to start somewhere - maybe some script kiddies are at their first Defcon and saw an easy target?

That's not what the parent said, they just said that the only thing that can take down GNU.org is DDoS

It's not simpler - quite the contrary. Dynamic sites can be taken down by a number of different attacks. Static sites are a much harder target.

It will DDoS your wallet with CloudFront charges which is even worse.

They just need to hit you over a longer time scale and avoid making obvious peaks so that you can’t ask for the DDoS refund.