The most of us pay to have something some is internet,a new tv,a new car,paid tv channels,porn,all those you spend money ,some turn into material you use the thing you pay,gambling is the same you play if you win you happy if you loose you can keep happy ,atleast you had tryed,nothing wrong on that.
But I think there at gambling when you spend some money and you lose there then you do not buy something entertainment but you buy tension and depression for your mind, and harmful things are considered as forbidden by nature.