BHD
Every business passes its costs on to its customers. For example, when a supermarket expands or renovates in order to carry more lines, who picks up the tab - all the customers and not just those that buy the new lines. Similarly with an airport - all its cunstomers pay for improvements even if not all benefit directly from them.
BHD management will have looked carefully at this investment decision, as it has done with all the other improvements over the years, and taken a view as to whether the market will allow it to recoup the cost in a reasonable timeframe. There is no way it will have done so on the basis only of Ryanair.