It's probably their own way of honoring Bitcoin or the Genesis block, the starting point of everything running right now. Of course, you can't do that if you don't have much. So, yeah, the ones who did it are indeed filthy rich, but it's not necessarily showing off. Nobody knows them anyway.
Or, I hope not, these could be erroneous transactions.
The third reason is to get profits or to sell their products.
What do you mean? You're sending a significant amount you can't anymore retrieve. How is profit made out of it?