Why is every one on here so about "gun oil"?

I remember in hunters safety years ago them telling us to put a good thick grease on the end of the bolt..... I've used about every oil out there at one point or another. I've used wd40 on a gun i dropped in the river. I soaked it in d40 to push the water out, then wiped it down. hunted for three more days and it worked fine. when i got home i completely wiped it down and re-oiled with gun oil. it worked well to get every drop of water out. it's your gun use what you want. I have an OLD semi auto that right in the manual it says to "use a good lubricating petroleum product, like Kerosene" KEROSENE! Any oil will corrode shell casings making it dangerous. I like using thin oil on my semi autos because they seem to function better and faster. ANY oil is better than no oil.