Because it's so damn good? And addicting and you want more? Like after i finished it i didn't know what to do with myself? I literally mopped for a week then i just read the manga. Twice. Saw all 3 seasons 4 times. My pinterest anime board is 70%(if not more) Haikyuu. I wanna see the stage plays cause more haikyuu? And high key crush on Oikawa's actor like DAMN BOY HOW ARE YOU REAL?!