@o_e_l_e_o  stated all the possible reasons why people make such transactions, and I would agree that it is probably mostly for the reason that people throw money into fountains, out of sheer superstition that something like this brings good luck.

What I would add as a reason is that some may think that Satoshi will one day show up and send them something back, and as far as I can see all these transactions are very symbolic, even below the $1 value. It’s like some kind of lottery for the future, or so it seems at the moment.