https://www.uspto.gov/trademarks-application-process/search-...
The trademark codeguru is not deposited by anybody, neither CodeGuru nor Amazon did their homework. Anyway the 20 years of usage should have precedence over just depositing a trademark.
You'd still run the risk of Amazon just not looking it up or caring, but the legal grounds would be much more on your side, abet I agree that 20 year precedence should be strong enough in itself.
That's fair. However a few hundred dollars could still be quite a lot. Especially for a small website or an open-source project where this could be basically all their donations.
In codeguru.com's case however, I'd grant you that they probably did have a decent enough income to afford a trademark registration, just maybe not when they started and by now it really wasn't on anyone's mind.
Maybe there needs to be some sort of a collective trademark ownership org small projects and sites could go to, which wouldn't sue somebody proactively for i.e naming their GitHub repo similarly, but would come up when legal at these large companies was running the name of their new product past existing trademarks.