Spice Jet Airlines — Charges for Airlines seats

Why we need to pay for the seat charges after booking flight tickets by paying hefty amount.
Are we paying just to stand in airline this is utter disgusting and disappointing.
You greedy People want to suck our money where ever you all can.
Give us one single reason why we need to pay for seats after booking tickets.
And while doing web checkin there is no single seat where you are not charging money and that too 1000 extra.
We need our hard earned money wherever you and the airlines are sucking from us.