Picked that one up couple of weeks ago and not sure what idea is but could mean BCN may come on in near future.
Highly doubt it
A simple marketing trick, to get more customers. "You don't fly to Barcelona?!" "Sure we do - pick the airport!" Nobody wants to go to Gerona. Everyone is looking for Barca.
And, well, a usability improvement to the website, after all. If they were to show the flights for both - Gerona and Reus in the same screen, to let me pick the cheapest one - it would work even better. For me, ofc, not them.