Then why is it Bridget Jones’s Diary and not Bridget Jones’ Diary?
Because Hollywood is clueless?
Just because you can find an example or two of an error does not change the fact that it is an error.
Irregardless, the irredundancy of this conversation is irredundant. Relevantly speaking, that is.
(Just a couple of common examples of other peeves that are commonly accepted errors).