Counterpoint: the arguments are fun.

Some people care about trying to find out the author's interpretation. I share this urge and cannot explain to you where it comes from rationally. It just is.

Also, what canon is and thus what author intent you could try to glean from that could be important, especially if the author is dead and can't clarify their intentions. Historians looking at influential media probably want to be able to tell what kind of message they were trying to send or what messages they were inadvertently reflecting. So whether a character canonically did something that reflects a certain historical viewpoint (author trying to send message), or fandom liked the idea but it was never canon (here were the popular attitudes of the day in that audience) might actually be important.

But yeah, for people not interested in fandom and not looking at popular fiction for historical sentiment analysis or whatever, I get how people could be annoyed. A lot of hobbies look pointless if you yourself do not engage in them and they are not immediately and obviously creating something new (woodworking, music, crafts, etc).

It matters for the infinite~~ly pointless~~ nerd arguments on who could beat who

Yes