U said it all here, just think about it for a second. If u need something u need to use some kind of paymant for that. For payment u need money/bitcoins. So dont u see its almost the same thing. Everyone like something, here people like bitcoins. Pretty simple, wasting time here, or wasting time on some 12 hours per day job on wind, rain, sun... well we all need some income.
For many of us this is a side thing, so why not to use my free time to try to earn something on nice and comfortable way (sittin in may chair, drinking something, smokin a cigar..al that in nice and hot room).
In my case its nice way to earn something for gambling. I dont spent my money, just what I earn here and on internet and its pretty fun acctualy.