This is true, but not for the reason you think (skip to the end for that...):Enormous cost of conversion is one reason, but that is secondary to the major reason: Familiarity with the USA units.
Neither construction industry engineers nor construction workers are stupid. But they are stubborn. And more importantly in your particular industry, they are cloistered. But in other parts of the construction industry (I'm in HVAC, pharma specific) we don't have that luxury, so I'm fluent in both. The phase-in would take time, but I learned SI in elementary school in the 1980s, so based on that the majority of today's workers should be capable of both.Every layperson, engineer, construction worker, etc. knows how much an inch or a foot is( About the length of an adult male's shod foot) . But how much is a meter? Not many know. So the construction super calls me the engineer on the phone and asks 'say there, Phantom, how much should I stick this foundation above the ground? It doesn't say on the drawings.' And I answer 'oh, sorry, stick it up about 6 to 12 inches" and the super says thanks and that's it. Now if using SI, and the same question is asked, I'd have to mentally or with calculator respond after several minutes 'about .15 to .3 meters' , hoping I did the conversion right without slipping a decimal point, and the duper would respond' huh? How the heck much is that?' And I would respond 'about 6 to 12 inches' and he is very happy and so am I, relieved that I didn't have to recheck my metric calc. Same goes for building materials be it steel or wood or concrete ; we all as engineers or fabricators know instantaneously that A36 steel has a yield strength of 36,000 pounds per square inch....I can't imagine specifying it as 200 MPa or whatever it is, hoping I didn't mean 200 Gpa, both of which are wrong anyway.
Converting back and forth is indeed a pain, but the pain would go away if you go to all SI. There is no issue of intuitive familiarity because you aren't eyeballing the measurement anyway, you use your SI tape measure without conversion!
The most difficult place for the conversion that I can see is with speed limit signs, since they don't have units on them. As a result, you'd have to replace signs multiple times over a generation to do the phase-in otherwise there is a safety risk. That's the type of "why bother?" effort that I think doomed the conversion to failure. But it is short sighted.On the contrary, in civil engineering, its moving backwards. 20 years ago, the government mandated SI units on state and federal highway plans...