If you’re looking for some logic in this mess, it’s that we generally use metric for things regulated by the government and imperial for more informal things.

So road signs and food package sizes are mandated to be in metric, so we’re forced to learn kilometers and grams there. But measurements of people and cooking temperatures are mostly used casually so we’ve stuck to old habits.

This leads to some ridiculous situations. For instance, we understand distances and fuel volumes in metric, but for a long long time we’d only talk about fuel economy in miles per gallon. Anyone who wanted to calculate fuel economy had to memorize the formulas to convert km to miles and litres to gallons.

Around me, this has finally changed in recent years and mostly it’s just old timers still using MPG. (Which is good, not just because metric is easier in this case, but because measuring economy as a ratio of fuel over distance is just plain superior to the other way around.)