It's because you can't reasonably put everything in the rules. They would be thousands of words and still have holes and special carve-outs, _and_ users will st

It's because you can't reasonably put everything in the rules. They would be thousands of words and still have holes and special carve-outs, _and_ users will still argue about rules application if you say your rules cover everything. It's more reasonable to have "a spirit of the law", so to speak.