It’s not hypocrisy because the signs they’re talking about are not in the same places as billboards. There are regulations about how far back billboards have to be. The signs in question here are the ones that are actually over the road or literally on the side of it, not 20 yards back.
And part of the reason that they don’t let billboards just hover literally over top of the roads is because they’re distracting. Signage that is on the road needs to have an official purpose and convey information that is relevant to the driver, and that information has to be delivered in a simple, uniform, and clear manner.