I've been on this flight twice and it's been packed and I have another one coming up in April that also looks very full. Late August until the week before Christmas is a very slow travel season for Hawaii in general so it makes sense to cut back the flights during this period. However, the non-stops re-appear in late December so it seems they are not discontinued, only "seasonally-adjusted."
BTW-as someone from the DC area, the Caribbean is NOT a first choice "warm" destination for most residents.