They're reliable, simple, cool-looking utility vehicles that represent American manufacturing capabilities during WW2. I also think they're a symbol/representation of how people and companies from all over the country came together in unity to win the war.
That probably sounds wishy-washy but my point is that they're a relic from a bygone era. Even when you look beyond WW2/Korea/Vietnam you'll realize that they were almost uncontested in the civilian 4x4 market for a few decades. The modern ones are terrible though.