Seems like this would be a pretty open and shut case of copyright infringement.

Pursuing something like this would perhaps cost more than 200k in the US. And then the startup would likely just fold and you get nothing in return.

Sending a DMCA takedown notice is free.

Unfortunately law being too expensive to pursue makes it practically non-existent. All IP/copyright etc. laws are complete bs because of this.

A large corporation can just roll over you and then say sorry and maybe pay some pocket change money

Hire a lawyer to send a legal notice. Costs practically nothing and since it's an open and shut case, free money for the lawyer (if they charge based on damages), or the startup caves and shuts down.

Absolutely. The lawsuit probably wouldn't get very far when it comes to damages, however...

I believe that BusyBox sued over violations like 17 years ago. I am not aware of any other instances.

Wikipedia has a list https://en.wikipedia.org/wiki/Open_source_license_litigation

Software Freedom Conservancy is currently suing Vizio. The interesting thing about this lawsuit is that it aims to make it possible for any recipient of GPL code sue for compliance, instead of requiring the copyright holder to sue.

https://sfconservancy.org/copyleft-compliance/vizio.html

It's always possible to try, especially as it seems there was a technical violation here, but whether it's worth it or likely to gain enough legal traction to yield results is another story, especially in instances of "your AI generated boiler plate looks like my AI generated boilerplate, and therefore is theft"