I think one of the reasons Formula 51 (51st State to you UK guys) was so popular to most of us as a film is that it shows a character wearing modern kilt wear, and not just a kilt in a formal scene. We have a lot of glimpes of kilts in formal settings, and a few historical (accurate or not) films in which kilts can be seen, but Formula 51 is the first film I have seen that the central character wears a kilt in a casual way. The kilt is also not the main focus of the film even thought it is an interesting, but irrelevant part of the story.

Duncan was great on Monarch, but he was also a bumbling boob at times. I don't think the average American household is ready for a kilt wearing main character in a TV series. The kilt would have to be a running joke (and insult) for the show to get acceptance on mass produced mindless TV.