So I think we can pretty much answer the OP's question.
The US are not fully metric because their industry betted on the wrong horse. They didn't see the obvious advantages of a system of measures based on the latest technological and scientific achievements and decided to cling to tradition.
What advantage does metric offer to the average person walking down the street? Not a darn thing! Some of our industry has converted, some more might convert, some never will. So what?
Second, despite our backward system, we have walked on the Moon and nobody else has and we did it 50 years ago. Some of the work was calc'd in metric, most of it was built in customary units. Call back when you leave footprints! In the meantime (probably another 100 years or so), keep working on the project, you'll get there someday, but we'll be on Mars before you get to the Moon!
While the other nations are now reaping the benefits of this move, the US will have to pay a high price to switch to modernity. That's why they are doing it peacemeal. The whole world is über patiently waiting for them to take the plunge but, meanwhile, can only shrug and go on with their lives.
Why do you care what we do? Why is this all so terribly important to you? We don't care what you're doing, we certainly don't criticize your use of the metric system but we're not staging protests demanding change. We simply don't care! If we need metric, we use it. If we don't, well, we don't. It isn't important in our everyday lives.
And do be aware that, as backward as we are, we're still the largest economy in the world.
Been to the Moon, largest economy in the world, Imperial units... See a pattern here?
My hunch is that the US will be metricated to a satisfactory extent in the next 50 years, or when California decides to change. What happens first.
Satisfactory to whom? It is already satisfactory to us and we're the only people that matter. We haven't converted at the population level in the last 50 years, why do you assume we will to it to your satisfaction in the next 50 years? Do you imagine that we care what the world thinks? Your only option is to redefine your idea of "satisfactory" and imagine that what you see today meets your new standard because what you see is all you'll ever see. Industry may change, science and medicine have changed or always were metric but the person walking down the street isn't going to change - ever! And certainly not just to meet your "satisfaction".
I know, every time I bring up the Moon thing people frame it as American Exceptionalism. Well, yes, it's true. But if it wasn't for AE, the French people would be speaking German and the standards would be in Berlin. The Germans always did have the superior scientists.