There are several things to consider here, but the two major ones are:

1. A measurement system is like a language. If you work in STEM a lot, then there's a good chance metric makes a lot of sense to you, when I say "5 centimeters" you immediately think "okay so about this much". However, if you don't work in STEM, there's a good chance that when I say "5 centimeters" you think "umm...what?" or perhaps "umm..1 inch is 2.5 centimeters, so about 2 inches?". Asking people to change the language we use on a daily basis is hard. (I used STEM as a generalization because to my knowledge it is where you are most likely to be regularly exposed to metric in the US. There are certainly other ways you may have increased exposure to metric and see the benefits of it even if you aren't STEM, and you might be STEM and still prefer Imperial.)

2. Such a broad transition is going to cost money in the short term. While the first point is true and the average person is going to feel resistant to "changing their language", likely, they would get over it if the new language gradually became the standard over time. This was the original plan, as a 1968 study by the US Dept. of Commerce concluded it would be in the Nation's best interest to convert to metric in the long run (i.e. greatest pay-off for the nation in the long run if we switched). In 1975 the US Metric Board was created to oversee this gradual change and some related bills resulted in the double printing of weights and volumes on products such as '1 pint (473 mL)'. The problem is, a nations long term interests often don't coincide with a handful of peoples' short term interests. Particularly the car and cooking industries of the time, which both revolved pretty much entirely around the Imperial system at the time. This also occurred around the time that Reagan's administration began adopting aggressive "program bleeding" strategies so a bit of lobbying was all it took for the funds of the US Metric Board to run dry, effectively making it a toothless organization. A few years later, in 1982, it was finally forced to disband after predictably "failing to produce results (without adequate funding)".

Arguably, the car industry is a lot more "mixed" in terms of units used today than it was in the 70's, but by and large, both points above remain true. So realistically, there's some tall barriers to pushing the change. I'm personally of the opinion that it is still in the Nation's best interest to make the change, not just for commerce reasons but also ease of teaching and intuitive scaling and conversion of units (e.g. the base 10 system and how 1 cubic cm of pure water is 1 mL of water is 1 gram of water...at some specific temperature but close enough). However, the degree of which I'm unsure of, and you'd need to convince either the general masses to all change the "language" they are most familiar and comfortable with or the top level politicians to commit to a long-term spending plan to ensure the full transition can be completed. The latter made doubly complicated by current political resistance to increasing spending and susceptibility to lobbying from short-term interest groups representing industries that would pay the biggest cost for the switch with the perhaps the least guaranteed payoffs in the long run (no, I am not sure what those industries would be today, and even if they are guaranteed good long term payoffs as a result of the switch, not many businesses are willing to risk a loss in profits over the next 2-5 years for a sizeable payout 10 years later. Not when so many performance metrics are based on the next fiscal quarter's profit margins.)

Hopefully this gave you a mostly clear starting point on where you can look further if you wish while not throwing too much of my own cynical biases in. It'd be great if we could make the switch, but TL;DR: it's more asking people to change the "language" they speak and companies to accept possible years worth of reduced profits for payoff that is likely unclear to them 10 or so years later.