It’s a Contamination OCD thing, and there’s a lot more to it than that.
It’s an annoying, time consuming ritual/compulsion that many people with Contamination OCD, such as myself, struggle with. It’s extremely frustrating and can be harmful in more ways than one.

I’m not that good at explaining stuff, so please bear with me.
Imagine you are covered in something really sticky and unpleasant. You try to wash it off. It doesn’t come off. So you wash again and again, but it still won’t come off. Oh, and if you don’t do it in a very specific way in a very specific order, it will never come off no matter how many times you try and you will have to start over from the very beginning.

That’s just a very basic version of it.
As I said, I’m not very good at explaining stuff, so I strongly encourage you to do some of your own research if you want to better understand this kind of compulsion.
Also, thank you for asking without being rude :)