Either they don't suggest it, or 'to make money'.
It has affected you, but it really is rare for anyone to do this and not attempting to be sexual with someone again because of it isn't helping you.
If lots of masturbation over many years reduced the size of a penis, I wouldn't be able to see mine... No, it's not harmful. If you only do it one way, it can make it harder to learn to orgasm from other things, including partner sex.