A couple of other viewpoints, from someone who admittedly has never written fan-fic, and has read only minute quantities.
Is it lame or pathetic to enjoy creating a watercolor painting, but not aspire to selling one’s art?
Or to be content making movies for public access television and not aspire to Hollywood?
Or to act in a community theater production and not aspire to Broadway?
Or to sing in a church choir and not aspire to be a soloist (let alone aspire to be a star)?
Or to enjoy cooking gourmet meals for your family and not aspire to be chef of your own restaurant?
Or to play in a recreational softball league, or pick-up basketball game and not aspire to be a pro-athlete?
Or fly a small airplane (like Broomstick has been doing) and not aspire to be a pilot for the airlines, flying big airplanes?
Or climb a mountain, but just an ordinary mountain, not aspire to climing Mount Everest?
If the answer to some or all of these questions is “no”, then why is the writing “equivalent” lame?
And the other point of view, which got typed while I was off doing other things, but not quite in my words. Writing fan fic seems to me to be a form of writing with a low threshold of difficulty. I might think about writing a great novel, but then I think “I’d like to write a story about a girl who communicates telepathically with a dragon” but how do I make it not sound just like Pern? Fan fic solves that problem. It can be Pern, or Hogwarts or wherever. Rather than having to start from scratch, one can start with a world someone else has dreamed up and build on that. Fanfic isn’t an invention of the internet–but it proliferates on the internet, because it is easy to share and see what others have done. Especially if one is not convinced that one will ever have something worth trying to sell.
So, yes, it is arguably lame–but the mistake you may be making is in not thinking of it as an end in it self, a knowingly limited form of writing, a way to pass time that otherwise might be spent in other meaningless tasks. There are people for whom writing fanfic led to writing original fiction and then to being published (Lois McMaster Bujold, for one) but there are others who may never be interested in dealing with the commercial side of writing, who nevertheless enjoy creating a story, and who may find more audience, or find themselves less intimidated by connecting someone else’s dots, then by staring at a blank sheet of paper.
Does that help?