Why do guys keep things from you?

I remember talking to a guy and he kept my keychain lanyard and every time I would ask him for it he refused to give it to me (he wanted something with me and I didn’t, I would always remind him lol) he also kept a sweater of mine and then this other guy I talked to kept one of my bracelets. I have never been in an actual relationship so I’m kinda confused when it comes to these things lol