A lot of the time code requirements get changed because someone fucked up so hard local government was forced to actually clock in and do work. It's also worth keeping in mind code isn't a ceiling it's the floor. As in it details the most half-assed way to build anything and have it still be legal. All of that said I'd love to have a word with the folks that have decided 3 acre minimum tract sizes locally are a requirement to put in a mobile home. Talk about defeating the purpose...