Why do helicopters pilots sit in the right seat in a side by side arrangement?

it is not necesarilly that way. russian helicopters follow the captain to the left seating.

it is more of a customary setup.

on the other hand, when seated right, you have your left hand free to control the nav and radios at the central console..

your left hand is controlling the collective lever, while your right controls the cyclics.

you can afford to release the collective, while you should keep the control of cyclis at all times.

I was told years ago, not sure if its true, That the direction of the main rotor head in relation to the fuselage would cause the helicopter to spin to the right if something happens to the tail rotor and the pilot would be on the inside able to see the landing area

Helicopters have controls on both sides, so you can sit on either side.