It's not mere convention. Reading the most significant digits first lets you abbreviate in an ad-hoc fashion and it also supports adding more precision as the n

It's not mere convention. Reading the most significant digits first lets you abbreviate in an ad-hoc fashion and it also supports adding more precision as the number is being written. "Most significant digit" is a clue that those are the figures people consider most important in general. They want to hear those digits first, abbreviate or round to those higher place values, etc. So, big-endian makes a lot of sense for writing and speaking. Little-endian really offers no advantages for speaking or writing. And in doing arithmetic, decimal answers expand in either direction (multiplication to the more significant, division and roots to the less significant), so you can't say one form is universally preferable there either. So big-endian wins!