The point is that you can see
this lottery as a cruel horror. You immediately hate it. It's obvious to us as the readers because it's outside our experience. Of course we wouldn't regularly just draw lots to stone someone to death, that's crazy and good people wouldn't put up with it, right?
What are the lotteries you don't see, because you're used to them, and they're just part of how the world works, like this one is to the people in the story?
If you're looking, you can find them. But it's also as uncomfortable to find them in real life as it is to read the story. So, most of us are happy to keep some other ideas between us and these lotteries. Those people just didn't do the right things. They should have been more careful, more prepared, more like the people who didn't get stoned. They should have done it the right way. They should have known their place. And if it's their time, well, what are you gonna do, mondays amirite?
And if that's true, then you can be safe because you will do the right things. And nobody has to go to the bother of persuading a society with any changes at the margins on which it sacrifices random people.