They may be lost for a reason. Whoever holds those rights may have forgotten them because nobody wants to read those books. Maybe they are boring, badly written, or in the current case, just a kind of literature that’s totally out of style.
If they were dated, but brilliant, there would be at least some market - Jane Austen is still in print, despite not being Danielle Steel. So no, in my opinion, being obscure is not the same thing as “copyright limbo” at all.
