Such as getting almost infinite caps etc.. Who does that? It's a single player game, you get no advantage over anyone, you just mess up your own gaming experience...

Can someone please explain this to me?

Well, it can be fun depending on the game. Like, sometimes giving yourself enough money to buy the strongest weapon early, and running around slaughtering everything in one hit, can be really entertaining/amusing. Sure, it can get boring eventually, but some people like it.

Alternatively, it 'gets rid' of a boring grind. I know I've played a few games where getting money felt like a chore, so never having to worry about money again removes a boring 'feature' and lets you focus on the 'fun' part. You do need a bit of self-control there, since you can easily run into making the game too easy, but...

Everyone enjoys gaming differently, so... And since it's a single player game, what they do themselves doesn't really matter since they can't come and hassle new players or anything like that.

I haven't used exploits, but have broken the economy legitimately (purified water is liquid gold). It took a lot to build all those purifiers (999 water at the beach = 500 to 800 bottles (8 caps per bottle) every 3 days. I did this because micromanaging 20 settlements almost ruined me "oh look a legendary ghoul... I really hope he has a lighter on him" so I trade water for shipments of crafting materials.

That's why I did what I did, but it has taken away a lot of the game as caps are no longer an item for me. Other than when I'm building settlements I regret it.

People who don't want to grind for stuff or something. It's their play-through, their problem. Some people just want to have a play as effortless as possible (I know I want sometimes).