Because I find it funny, in the same way that cartoons are funny.
you know how some people find certain swimsuits to be offensive and others who have grown up around nude beaches dont bat an eye at swimsuits?
I've apparently been exposed to much more funnier things for a long time. simple sight gags dont register as anything more than any plain image. It's fine that they do for you, but it's also kinda sad that you haven't been desensitized to it because it means your exposure to funny things is way lower than it could be. and given the state of the world, getting that high quality comedy in is quite beneficial.
Also, it's funny to warp a harmless picture of a flashlight thru a dog into a horrific story of animal abuse and death when it was entirely intended to be some kind of lighthearted random nonsense post. Especially when someone takes it seriously.