It's "seen as" sacred because most guests don't question the "story" imposed on the land and either turn a blind eye towards or are ignorant of the anachronisms. (Just like so many bought into the idea that Haunted Mansion has a coherent narrative, which it most certainly doesn't.)
As mentioned above, the colonial-time land has: a Gothic Mansion, a Mississippi Riverboat and port, and a Western saloon (Diamond Horseshoe). Not to mention a Christmas shop which has no colonial Christmas items since the colonialists really didn't celebrate Christmas in any way like we do today).
And Frontierland has Southern bears singing 20th mid-century songs, and a Splash Mountain with a Frankensteinian fusion of Southern and Wild West themes, and a Mississippi Riverboat.
Do CMs giving tours still try to sell a small band of brown concrete as the Mississippi River separating the East from the West, while, at the same time, they claim the brown concrete is also open-air sewage and there's already a Mississippi River and Riverboat right next to them?
Anyhoo, all these inconsistencies don't matter much to me... until someone objects to PatF because *that* is what will introduce an inconsistency. Yes, there should be no inconsistencies, but until WDW/WDI wants to address the pre-existing ones with a major overhaul of the lands... what's trading out one inconsistency for another?