I've been giving this a bit too much thought, so I think:
Because as I mentioned earlier, it's messy, some people don't like or can't eat spicy foods and it's a bit samey plus you have to take into account different heat level tolerances/preferences.
If I were having a big party, even though I've got some pretty massive pots, none of them would feed 30+ guests. So the chilli would probably be one of a few options and it wouldn't matter that some people don't like spicy food. If I were having a small, but casual party, I would either know what my guests liked eating, or I would ask them. If OP were coming round, I wouldn't make chilli!
It's not that messy in my opinion because you can eat it from a bowl with one utensil. I wouldn't serve it with jacket potatoes (as some have suggested) for a big party, because you'd need to be able to cut those up. Someone earlier suggested they'd rather have lasagne, which again would need cutting up and is therefore not an option unless it's a small party with space for everyone to sit down at the same time and put their plate down.
However, when I have parties I make not just one, but multiple massive salads of all different kinds (can be made ahead and/or dressed at last minute), a cheeseboard, and lots of cakes.