It's mostly because it allows you to put code at a fixed address at the beginning of the memory and the stack at the opposite end. That lets the OS place the st

It's mostly because it allows you to put code at a fixed address at the beginning of the memory and the stack at the opposite end. That lets the OS place the stack at a constant address (for MS-DOS COM files the stack pointer starts at 0xFFFE, with a zero already pushed so that a RET instruction exits the program; a similar convention existed in CP/M).