A big driver of going the PRNAV way is ATC procedure design. It simply costs way too much airspace designing those nifty arrival transitions and departure routes within the limits of BRNAV (which is equivalent to RNAV5). If the transition downwind and inbound are 3NM (heard 5NM somewhere) apart they are PRNAV compliant, to design the same in BRNAV requires 5 times more space.
But yes, it does hurt airlines as well, however they do have some more or less clever ways around it. We had to get PRNAV approval on our 737 classic fleet for its last 3 years, which required us to get new FMC boxes at around 100k$ per plane (to upgrade the memory from 192kb to around 1MB). There is simply no business case to make up that kind of money within 2 or 3 years, but there is the possibility to lease those boxes, which is what we did.