Because they appear to be building at SOU so makes sense they transfer all of the established GVA flights there. No one is flying from BOH that won’t want to fly from SOU. If I was SOU that would be the first thing I would be persuading EZY to do. People need to associate SOU with EZY and that’s hard to do if there is a spilt operation locally. When you think of BOH you think FR.
I don't think you understand how things work - the airline will go where there is money to be made. Look at where Ryanair fly to from Stansted and Luton - Kerry, Dublin, Cork, Kerry, Kaunus, Alicante etc. etc. By your logic they wouldn't do this would they?