This is not a scientific fact, this is just my opinion, but I think that it is just a habit. Like biting your nails. Also, if you hang around others who swear, you are more likely to. Just like an accent, when you hear people speaking one certain way then you speak that way too. If you want to stop swearing, I suggest you don't hang around the others who swear and start "punishing" yourself everytime you swear. For example have a jar set aside that you will put a quarter in every time you swear. Your whole family could do that if you all have a swearing issue. Just a thought. :)
Because your used to it
Cause you have a potty mouth and you just can't help yourself.
Probably because you have a big boasting and babbling mouth.