It's just nostalgia. As someone who grewup in the mid atlantic, then spent ten years in LA, and now lives in Maine, I would take any old run of the mill strip mall Cambodian donut shop in LA over DD any day of the week (my local was one at Sawtelle & Santa Monica in West LA).
Luckily in Portland we also have good local stuff like
Holy Donut.
Only reason to drink DD coffee is for a road trip. Again, nostalgia paired with easy access (hello rest stops).