cuz stryde sniper is love, stryde sniper is life.Kinda like what silent aurora said, Its hard to move on something your attached too.
I've stayed because I know that this might be the only thing I will be good at,
I liked playing the game, and I still do. Knowing your good at the game, its a great feeling.
When I was in Egypt, I didn't even know about top 100, or stryde SNiper, or cared about it. I played approved maps and custom, and had one hell of a time.
I moved back to America, And I thought about playing ranked and getting good, But the thing is Ranked snipers was much harder in Wash/Cali than Approved maps in Eu Server, so I was determined to get good.
I did get good, and i'm in the top 20 now

One other reason is because This is a game that my crappy computer can run
Sure if I had a good computer I would play other games, but I wouldn't play this one as much.
This is a Great Flash Game, and deserves more attention than It ever has gotten.
Pewdiepie should make a video, even if he hates it, it would get attention.But yeah, thats my reason.
tl;dr - Because this game is awesome and hard to master