I prefer to get outside the system--here's my comment:
Alternate theory: Language keeps changing, but needs to be kept stable enough to be useful.
It's both good and natural to have people pulling in both directions, according to what usages feel plausible to them.
I'm not sure how much language change comes from great writers, how much from slang, and how much from mainstream drift.
Second thought: I'm not sure how much the important resistance to change comes from people who invoke rules and stability and how much is from people who just don't use the changes they don't like.