So we want to measure energy - how shall we do it?
We could use the English system and choose one of about a hundred measures including British Thermal Units, Foot Pound Force, Horsepower per hour etc of which there is an arbitary conversion to the others somewhere....now where did I put it again?
Or we could use SI units and have the same measure no matter what sort of energy we are measuring. There are no arbitary conversions, each unit is compatible with the others and we don't have to mix up conversion factors all over the place.
It doesn't matter who invented it, it works so well that is is far superior to Imperial measurement.
Having said that, re-tooling is very expensive and the transition very hard, and people are used to the system of measurement they were brought up with. It certainly sounds better to say "quarter pound" than "about 100 grams". Also, in various places, non SI units are very valuable, like Knots for navigation. In the end though, people do get used to new units and the SI system has such value it is worth considering.
Also, even if you did make your manufacturing in SI, what standard thread would you use? And what head for your screws - Phillips, Cross head, Posidrive etc. Standardisation goes on and on and on. Sometimes it is a blessing, other times a curse. Often its better to stick to what you know.
And 411A - I'm not envious of your measurement system at all - I just think its too unwieldy. Your arbitary use of a gallon being 3.78 litres is just as arbitary as the English gallon being 4.54 litres - neither is better.