Well, that's not exactly how it works. You don't even need to register a trademark to have common law rights to avoid source confusion. You have to use the mark

Well, that's not exactly how it works. You don't even need to register a trademark to have common law rights to avoid source confusion. You have to use the mark though or you lose the rights, that much is true. But the only way you lose the right to enforce altogether is if you have some kind of unregistered mark and let it expire. And even if everything you said was exactly right, they still don't have to enforce the trademark in every case to protect their rights. As long as they keep making Rust, they own the rights to call a programming language Rust and they have the right to be identified as the official source and as long as they perfect their rights, they can use it to stop others from using it in certain cases, if they want. There's not really a "waiver" issue except in edge cases. Things only become "common names" in the case (or at least it used to be) that they become generic terms in the language, like "Hey, go xerox this, get me a kleenex, and then google something." Rust will never be able to expand its mark quite like that because it is a generic term in other uses, such as iron oxide. They will not be able to control the production of iron oxide or who calls it rust. So the whole "that's just how this works" defense is either one given by an apologist or someone who is just wrong.