why hasn't the usa switched to metric yet?

Tradition and inertia. I've also heard theorizing that it has to do with Imperial units being easier for humans to think in, with scales that make more sense to human minds, but I suspect that's familiarity more than anything else, at least until I hear from people who grew up using metric saying they have a harder time judging distance than Americans. Personally, being an American, I am familiar with and think in SI, so wouldn't like switching over. This is despite being a physicist who does a lot of calculations in metric because it IS easier to do math in, and then having to convert to SI to get my head to picture the values in real-world quantities.

@Segev As a Canadian who grew up with metric, I don't have issues with it. Imperial is confusing to me lol. Although we still use imperial for things like construction, which is interesting. One idea could be that 12s (imperial uses those right?) are easier to divide evenly. They can be divided by 2, 3, 4, and 6 evenly which makes it much easier human calculating.

england is metric, but common usage is still feet and inches for heights, stone for weight, miles per hour etc. i hadnt heard of the idea that imperial makes more sense to human minds, thats interesting. i think its more to do with familiarity. altho a yard being closer to a man's stride than a meter is might be a factor? more 'embodied'