What I am about to say, obviously does not stand true for EVERYONE, however for many it is the case.

As you grow up, you start to get this mentality of needing to discard things that would be for "kids", as the impact of the society around you, and your quest for acceptance continues, you deem more things as "childish" and you start to act "more grown up". 

At some point, you will realize that what other people think about you doesn't matter at all. That you should embrace the things that YOU enjoy, for the sole fact that YOU enjoy them. When "being cool" is no longer relevant, you get to stop worrying, and start enjoying.