Spice Jet Airlines — check in problems

We 2 people are travelling together, and we are getting separate seats and it has been told to us that if we want to sit together we can buy premium. When we are paying for the tickets why do we need yo pay for even basic facilities. We need to pay for each and everything like window and aisle seats that means we are forced to pay extra if we want to sit together.
We will try to never go for spicejet.