Sin offerings are usually performed when someone has unwittingly got themselves into a ritually unclean state.
Having a baby, having dry rot in your house the Kohen isolates you, performs the prescribed action and when you are in the clear kills an animal because God likes blood and burned animals.
But these things have a root in a personal or group divine retribution.
God has smitten you with mildew for some offense to his person (usually gossip), God makes your wife bleed because she is a woman and descended from a long line of scrumpers and you let he sit on a chair when she was on the blob so you are unclean too.
It's all rather daft but it's all part of the same line of progression which validates Jesus as the messiah so you really can't have one without the other unless you just write a new Bible.