Why did they order A319s that could take more then 150 people, only to decide a few years later they just want 150 seats. Did the market change?
You need to look a little deeper than that.....
by taking out six seats, they lose six lots of revenue per sector.....
They will increase the cost of the 12 adjacent seats to recoup that revenue as well as losing 1 member of cabin crew per flight.
The market hasn't changed, the demand is still there that they will see the same amount of people trying to buy a few seats less, increasing the fares and revenue, and saving costs by employing less cabin crew.
A clever move that will probably work financially, but will affect the service offered on board, by quite a long way.