CGN-BCN has been served by Germanwings for ten years now.
From a local perspective, I guess GRO can be seen as a destination in its own right rather than an airport serving Barcelona. If it were different, why does FR continue serving GRO at all now that they also fly into BCN?
Btw., in the past, there was also CGN-REU by HLX in addition to CGN-BCN by Germanwings.