It's that RA have gone to some effort
Trav - changing the unreserved seat assignment logic does not involve much effort at all. Should be more than possible to amend the software that assigns seats and test within a few days for one person. There was probably far greater cost to the company in the various levels of management spending time deciding whether to implement a new 'more commercial' seat assignment policy
Waldo - you're confusing sales revenue with profit. From a flight full of people, the average food/drink revenue on board is a few pounds, of which a fair chunk has to go in costs - namely buying the food/drink, loading it onto the plane, printing menus, cleaning the cabin at each turnaround, etc, etc...
A reserved seat has almost zero cost to the airline, and enforcement is usually done by other passengers - 'Oy, you are sitting in my seat'. Never mind if food/drink takes a bit of a hit, the profits from seat reservations will likely more than cover it.
As soon as the mainstream travel press across Europe picks on this new policy and publishes articles, passengers *may* decide en masse to start paying up for those seat reservations
In marketing speak, you are being 'monetised'