I take issue with the word "ban," because it implies that D&D is one, set thing and all campaigns are, at core, the same -- a simulacrum of the core rules.
I have always followed the premise that every campaign is different, every setting is different. To some extent, D&D is D&D - and every D&D campaign draws elements from the same tool box. But not only are there other possible tools in a given campaign (house rules, unique elements to the setting, etc), but every DM will utilize different tools, based upon the setting they've put together.
So it isn't banning, because it there's no one-size fits all version of D&D that we all play. Certainly, the official rules provide a default, but that doesn't mean that every game should assume to include everything in the official rules.
Maybe I'm nitpicking on semantics, but I think "ban" has certain connotations that implies that if a DM doesn't include certain elements in their campaign world, they're being restrictive.
I mean, it isn't unlike cooking - say, a soup. If you don't include every spice and ingredient in your cupboard in the soup, you're not "banning" anything. You're just making a soup with specific elements towards some kind of theme or flavor.