Capitalisation isn't universal. Languages like German capitalise every noun, so from a German perspective, Gram, Metre, and Litre should all be capitalised and it's the English that are wrong for using lowercase units.
Meanwhile, English capitalises stuff that other languages don't, like the names of languages, times (days and such), and for some reason "I". By the time the metric system was conceived, English still capitalised most nouns (just look at the US constitution for example) after very recently coming into contact with the concept of capital letters in the first place, something copied from German printing presses.
And then there are the many languages that don't even have capitals, which will probably question why there are two ways to write every letter when they first learn languages with a Latin alphabet.
Nothing "deserves" to be capitalised, every language just decided to stick to some arbitrary rules. There's no good reason why `Monday` is more important than `website`, or why `I` is more important than `you`.
Meanwhile, English capitalises stuff that other languages don't, like the names of languages, times (days and such), and for some reason "I". By the time the metric system was conceived, English still capitalised most nouns (just look at the US constitution for example) after very recently coming into contact with the concept of capital letters in the first place, something copied from German printing presses.
And then there are the many languages that don't even have capitals, which will probably question why there are two ways to write every letter when they first learn languages with a Latin alphabet.
Nothing "deserves" to be capitalised, every language just decided to stick to some arbitrary rules. There's no good reason why `Monday` is more important than `website`, or why `I` is more important than `you`.