Those have nothing to do with losing copyright. Forgetting to file for copyright, sure. But not losing copyright you have.
If you have standing and you don’t sue for lack of money, of course the infringer gets away with it! Your right was not extinguished though. You don’t have the right to bludgeon others, you have the exclusive right to copy.
Semantics... I consider the rightsholder generally acknowledging any infringement but not doing anything about any of it, combined with other people getting away with infringing, as functionally equivalent to "losing" the copyright. You might disagree but that's okay.
Try telling that to a lawyer. Not enforcing your exclusive privileges does not extinguish your rights. People don't lose the right to vote if the government refuses to enforce election fraud.
You are wrong in the legal sense, and copyright is a very legal matter.
I think you are assuming that by "lose" I meant indefinitely, and for any and all future cases... but I explicitly defined what I meant, which was the cases where the rightsholder was made aware of an infringement, chose not to litigate, and then the statute expired, leading to a functional equivalence of losing the copyright in that one instance. I think a lawyer would appreciate the detail, and I don't think I am on trial for my own semantics here either, so I'm not sure what the actual disagreement is, besides that you don't like the way I used the word "lose".
If you have standing and you don’t sue for lack of money, of course the infringer gets away with it! Your right was not extinguished though. You don’t have the right to bludgeon others, you have the exclusive right to copy.