We are really "not" not using metric measures
One of the peculiar realities anyone who uses measures a good deal runs into is the AVP/Imp/Metric schism. From a US point of view the differences between AVD and Imperial are much more confusing. Canada for instance uses Imperial Gallons, the US uses an older version that is smaller in volume. A US gallon is 0.83267 British gallons, a bit more than 4/5 ths of a Gallon(Brit) as Glover's Pocket Ref would put it. [The Canadians also seem to get milk in bags, which seems - well - Canadian.] In Britain you often see Youtubers using inches and feet, and the reason is that for some activities such as building furniture, "old money" is actually easier. The numbers are all smaller for example, and the fractions are common fractions which are fairly easy to deal with in your head, while decimal fractions are more difficult. 16 1/5 inches for instance is 419.1 mm. You can round that to either 420 or 419, but finding that on a ruler when you're older and the eyes are showing a lot of mileage is a fussy and frustrating task. A 1/16 inch is 1.5875 mm, finding the right 1/16th can be fussy and irritating as well, but if you are using the right scale, there WILL be a graduation mark there. Obviously you can work to whole millimeters and the problem should go away. However . . . using "old money" drawings means that you convert every measure to meteric, and because of rounding, errors creep in. You have to define a tactic to prevent the random noise of rounding from turning your build into a cat' cradle of odd angles - not quite square, and non-Euclidian surfaces - not exactiy flat, and places where things join oddly. You must in short employ a different kind of approach to measuring. It doesn't look that way, but it is.
You hear a good deal of metric disparagement of the use of a human body part, e.g. a foot, as a standard measure. The trouble with this arrogance is that it assumes a lot. Furniture, even metrically laid out designs still work to standardized human proportions. You'll discover that measures such as 300 mm, and 600 mm occur frequently (one and two feet more or less). This is because humans really are more or less standardized. The traditional measures employ that in ways that guarantee than most furniture will fit most people (not all), and where you have volumes, people will tend to feel they are not being cheated. To habituate from a gallon down to a liter takes practice. (Though many "traditional" volumes and weights are outright weird, such as a pipe, a tun, or a quarter).
What is more of an actual issue is that the measuring is the different arithmetic. The "old money" system uses "12" with simpifies a lot of fractions, because you get nice common fractions. That harks back to Babylon and Summeria where a hexagismal (bas-60) system was employed. This offers many more common fraction solutions and whole number results than base-10. The Arabs, and their heirs who divised the metric system, stuck to counting on their fingers. Apparently the Summerian decided that teams of three (10 finger and ten toes person) worked better.
Just to keep the AVDP/Imperial divide stirred, the US standarized the inch to 25.4 mm exactly. This still has its drawbacks I had a bureaucrat who tried to insist that we had made a mistake. The standard form devised by bureaucrats and would-be desk jockeys wanted both AVDP and Metric figures for certain things recorded in the field. They apparently had assumed they needed to check field scientist's arithmetic, and had discovered our metric areas were wrong. Their area estimates however were achieved by trying converting a square meter area to square feet using a linear conversion factor. When this was pointed out, there was a deafening silence, followed by an "oh." No apology or "my mistake." Note there that the "area" we turned in was a metric estimate. People and their preferences are _always_ more of a problem than any particular measurement system.