As I recall, Veronica was vain, demanding, selfish, thoughtless, arrogant, mean, tantrum-prone, and high-maintenance. A parody of a spoiled rich kid.
Betty was friendly, outgoing, helpful, kind, would do anything for you, upbeat. Did I mention sweet, supportive, fun-loving, and could cook, sew, and even fix Archie's car? (Also steaming hot but doesn't seem to know it.) So of course Archie took her for granted. He'll probably cry on her shoulder when Veronica makes his life a living Hell (and she will, oh she will...)
But then, the only character with half a brain in that comic was Jughead.