Off the top of my head:
Nobody questions why main drive is C:, remnant of [an] early computer having two floppy (not sure) drives on A: and B:
Or more recent - C:/Windows/System32 holds 64 bit executables; 32 bit exectuables live in C:/Windows/SysWOW64
Recently I was trying to install some obscure driver for a device that doesn't autodetect in my Windows 10 work computer, I had to go through the old school "add device" wizard. When clicking to manually provide the driver, the dialog is exactly (or almost?) the same as the one from Windows 95, and the path defaults to... A:\! There's no floppy on this computer, there even isn't an optical drive!