Why were the doors and walls so grimy?

They looked like they had many decades' worth of nicotine and general dirt/grime buildup on them. If the set designers/decorators were trying to make the paint look aged, they failed, because it just looked like it hadn't been washed in ages:

https://i.imgur.com/Ifp4jtJ.png

It was like that throughout the show's entire run.

It was strange because everything else in the Inn looked nice, but the cruddy painted doors and wainscotting looked like something you'd expect to see in Leatherface's house.