Sometimes the remnants of yesteryear are too far removed from the present to fully understand what they are, what they were for, or why they even still exist. Just imagine trying to explain to future generations that we once carried around portable music disc players, which meant having to carry around a library of music discs as well.
Not so portable, amirite? Not to date myself too horribly, but I'm old enough to remember buying a coat with pockets big enough to hold my CDs. Seems pretty silly right now.
So the past often offers up things that are legitimately questionable, like the structure above. Reddit user Koreshdog saw it on a beach one day and it had him pondering its purpose, so they turned to the site's r/whatisthisthing community, and as usual, they came through with an answer.