Bremen also for example: Ryanair only get reduced fees on routes not already served.
Ryanair were happy with the overall Bremen deal, so accepted it.
However, Ryanair are not willing to do such a "no cannibalism" deal with Belfast, or Cork, or Shannon for various reasons. I suppose they look at each deal offered in detail. A Belfast "no cannibalism" deal would not have interested Ryanair. That said, they are not competing directly on any Belfast route thus far. This winter no other airline will do BHD to LPL, EMA, PIK or STN.