The explanation give in the BA shareholders November newsletter is that it's all about ground facilities...not for aircraft but for travellers. BA withdrew because the DR was a low-cost destination for tourists. They have restarted to flights to PC because of the number of more upmarket hotels that have opened, presumably catering for the sort of passenger that would be prepared to pay business leisure fares on BA services. It's interesting to note that the BA language has shifted from business travellers to include premium leisure travellers.