The story I had heard was that it was characteristic of a competing tribe, but doing some quick googling right now it looks like the reason is more likely to be

The story I had heard was that it was characteristic of a competing tribe, but doing some quick googling right now it looks like the reason is more likely to be that such garments were reserved for priests - not sure why this rule didn't apply to them. At any rate, I am far from an expert on the Torah or Bible Old Testament, so maybe someone more knowledgeable can talk about what we think the reasons were for this law at the time.