I still see it applied for modes in chord notations, and it echoes the use of the distinction of M/m for Maximum and minimum in mathematical shorthand.
It might be a kind of political correctness: all modes are created equal, they should not be typographically discriminated. None of them should have an initial uppercase when others have only lowercases, c minor is as respectable as A Major, and there are other scales and modes.
A related question is do you use a uppercase or a lowercase "d" with Bach's Toccata in Dorian mode BWV 538? Most recent recordings do not respect Dorian as a mode, they only present it as a surname, like a dedication:
Toccata and Fugue in D minor, BWV 538 "Dorian"
Perhaps one will someday ask : Who was Dorian? And who was she to J.-S. Bach?