Ok, so then Halloween comes, and you get this steady stream of kids of all ages. Every once in a while, someone yells out "Trick or Treat! Oh, and I pre-registered!" And now the person at the door has to stop everything and check the list. And if the kid's on it, he or she gets "the good stuff." And this happens in full view of people who didn't know about the pre-registering bit. So they start asking. And now this family has a big crowd in front of their house; some are pre-registered, some aren't, some are asking, some are answering. But, as is the nature of large crowds passing along information, not everyone is getting the full story. So they're asking again. And some people are voicing their disagreement with the "policy." And some kids are saying they pre-registered, but their name isn't on the list. Or it's there, but it's been checked off already, so they're being accused of double dipping. So the next year, the family decides to install one of those fingerprint reading machines like they have at the entrances to the Disney parks. And then we find that some kids are pre-registering more than once and with different names. And if you didn't pre-register but you live close by, you can still get a good treat, but you have to swear that you are telling the truth and sign and have notarized an affidavit saying that you agree to the terms and conditions of the contract and you will give back the candy if and when someone is able to prove that you actually did pre-register AND already got good candy.
Honestly, this is way too much effort for something that's supposed to be fun.