From a roleplay/world building perspective, I really like the fact that Fallout New Vegas has an extremely limited radio and I do think the atmosphere would be seriously damaged if they had added more songs. I haven’t played the other Fallout games but I reckon this is probably applicable there too. I understand that people get bored of the same songs over and over again, but that’s a feature not a bug. If you were living a hard scrabble life a post-apocalyptic wasteland where no one has the means or resources to be writing, recording and distributing popular songs, yeah you’d probably get bored of listening to the same music over and over again. And then when you turn the radio off, all you can hear is the creepy horror sounds of the Mojave and suddenly listening to Jingle Jangle on repeat doesn’t seem so bad after all. The repetitive, upbeat soundtrack is super effective at making you feel like you’re stuck between two not so great choices, one awful and one somewhat better but severely lacking. And that really reflects what it’s like to live in the Mojave–you often don’t have the luxury of a completely satisfying choice because you and everyone else is fighting for survival. Specific to FoNV, it really drives home the political climate of the harsh, brutal Legion versus the comforting but stale and ineffective NCR. Honestly FoNV is the first game that really made me think in depth about the music choices in a video game and I’m really really glad they made this choice.
I am pretty sure though that the Big Mountain DLC added a new radio station.
TL;DR: swear words like “shit” usually emphasize the mood of a sentence rather than add new meaning, which is why “shit” seems to change connotation across your examples. Think like the word “very”.
Traditionally in most European languages, the cycle of what is considered most offensive shifts between bodily functions (shit, piss), genitalia and sexual acts (cunt, cock, fuck) and religious profanity (hell, bloody), particularly against the Christian God. Some scholars define us as moving into a new cycle, where the most offensive words are slurs based on race, sexuality, or gender. These scholars speculate that this results in more willingness to experiment with already existing swear words of the ‘traditional’ categories since they are considered less offensive in comparison.
Swear words are almost always used euphemistically and in set phrases. Some scholars go as far as to argue that swearing is only euphemistic and words used literally do not count as “swearing”. In fact, much of swear word usage can be classified as an intensifier, which is a word or short phrase that sort of heightens the already existing mood of the sentence but doesn’t explicitly change the meaning. Using shit as an example, “Shit, the bread’s gone stale again.” In this example, you can also see shit being used as a sort of mood marker, since it is reasonable to assume out of context that the bread going stale might be desirable to the speaker. In this case, the “shit” marks the stale bread is actually bad as well as intensifying the mood as compared to, say “oh darn, the bread’s gone stale again.”
This part is a bit of speculation on the origin of set phrases like “ain’t shit” or “the shit” and I haven’t actually read any scholarly literature on this topic specifically. You can see similarities between set phrases like “this is the shit” and “this is the stuff” and “that’s the spot”. It seems like this is a construction common in the English language to express that something is pleasurable. Whether this is what caused the “this is the shit” set phrase or whether the “this is the shit” set phrase caused the construction remains to be seen. “Ain’t shit” is definitely somewhat different because it probably comes from African American Vernacular English (AAVE). While I would argue that “the shit” could be AAVE in origin as well, I do think it has roots in non AAVE English, whereas “ain’t shit” is grammatically AAVE.
If you’re interested in reading more, I recommend The F Word by Jesse Sheidlower and Holy Sh*t by Melissa Mohr.