Guessing where your luggage gets lost is a difficult exercise.

You mention that you flew into IAD on DL1128, but that is currently flying into ROA not IAD and ROA, although in VA, is quite far from IAD (also in VA). But let's assume that you took another flight getting into IAD and that your bags were checked through. It seems to me more likely that your bags did not make the domestic/international transfer. That is quite common. Your bags could have be sitting there for a couple of days. Furthermore, the weather was particularly inclement in many states on Dec 22, so your bags probably had plenty of company.

I am not saying that I know where your bags were, but accusing an airline with such harsh words based on a guess might be too extreme. Why don't you also accuse DL? Furthermore in many airports, baggage handlers are employees of the airport, not of the airline. While each airline has some representative handling the claim, they are not running around the airport looking for your bag in every corner, airport employees do that.