yes, the instances of forking are about it being legally fine. nothing to do with the psychological overwhelming of forks.
I know that the work itself never addresses that, but it seems to me as though it's trivial to derive.
also, death of the author just means that the interpretation of a work is independent from the author's intention. nothing to do with categorisation.
Does the author having it categorized in a certain way not count as the author's intention?
[forks rarely become many] because people add plugin APIs/modification APIs. which makes making many forks unnecessary.
I don't think that's true. I think that forks rarely become many because most attempts to fork a project will invariably get absorbed into the main project or one of the few forks that fills a unique niche different from the original project. I don't think that a modification API helps with anything.