Stuff like this sign:
Because all those those people defecating all over Half Dome either didn't care, or didn't think one person's p00p could matter, and of course, one person's doesn't unless everybody thinks that, and then that's a lot of poo.
And responsible people sometimes seem to take these rules as a personal attack; they aren't, but there's a lot of stupid lazy people who need the rules. As the ranger explained to me at Yosemite, the reason they make you camp 200' from water is that in the middle of the night, when it's cold, and you're in your underwear, are you REALLY going to make sure you walk far enough that you aren't urinating in a drinking water source? Okay, so you might, but plenty of people won't, and we can't tell by looking who those people are and aren't, ergo the 200' rule.
As for burying food, it's acceptable to widely disperse the watered down bits and pieces left over in after you wash your dishes. But I camp in bear country, and I DO NOT want to worry that I set up my tarp over (or near) a spot where somebody buried (not deep enough) all the extra food they over packed and didn't feel like carrying out, and have a bear come visiting in the night because it smells food *in* my tarp. Again, YOU probably don't do these things, but other people do, and those are the people who need the rules.