(Possibly NSFW) Why are certain parts of curse words not allowed on TV?

It used to be that no curse words were ever heard on regular broadcast TV (in America). These days some are allowed, but I’ve noticed that they often bleep part of the word. I hear “damn” and “ass” pretty regularly, but never ”God damn” or “ass hole”. It seems to me that “God” and “hole” are not the bad parts of these “bad” words. What’s up with that?

Side question: Why do we tend to view some curse words as worse than others? Why are some words allowed on non-cable TV (“damn”, “hell”, and “ass” being the ones I can think of) and others not (“fuck”, “shit”, and “bitch”)?