Don't really know but I suspect it was because the Dublin name had been aglacised and was very much associated with British rule in Ireland. Both names seem to have survived a long time.

Dublin was also I think originally a Viking settlement where as B.A.C was originally built by the locals (or at least earlier settlers) and may therefore have been deemed to be a more pleasing name to those standardising on Irish placenames, who would have tended to be very nationalistic in their outlook.

I have some books at home which might be more enlightning here and if I discover anything there I'll let you know. Meantime there's probably someone out there with the correct answer.