To me, it's part satire and part arrogance. Some people find it so hard to understand that their memory can be faulty that they'll construct a whole theory around something in order to avoid doing so. Others capitalized on that in a humorous way to contribute further to the "Mandela effect".

Of course, the silliness has always been refuted, since nobody has an authentic example of "Berenstein" that isn't itself an error or misprint.

It also touches on the lack of care that people tend to have when it comes to getting names right. The creators of the Bears dealt with this in school, with a teacher who absolutely refused to believe that the A spelling was correct, asserting "there is no such name". A very large number of people throughout history have suffered similar fates, where others would dispute the spelling of their name, or indeed their entire name.