Gaming is still relatively expensive compared to other forms of media, so to say someone cannot be a fan of a game if they only have watched playthroughs is ignorant to the fact that some people simply do not have the funds or even access to every game on the market.
There is also quite a few games where I love the characters, story, art, music, ect, and just don't like the gameplay all that much, or I just ended up seeing more of it than actually playing. Video Games are more than just Gameplay, despite it being a big part of them.