It’s pretty standard practice nowadays for airlines to charge an extra fee for ‘premium
seats’ such as the bulkhead and exit rows. I usually balk at the extra charge which can sometimes be 50% of the cost of the flight segment and so do a lot of other people it seems, which is why they often go empty. Why pay though when you can get it for free?
My technique? I wait at the gate and be the last person boarding the plane. If the exit row is free just sit in it like you own it! 99% of the time the stewards don’t check your boarding pass and the worst possible outcome is they tell you to move.