it's more optimal when you're doing pipelining, for example adding two numbers to do the operation you start from the lowest byte and add them together and move up. With little endian bytes are already positioned in the order you want.

x86 architecture also was big on backward compatibility. You have registers that can be accessed as 8bit, 16bit, 32bit (and I believe 64bit) adding the extra bytes after similarly makes it easier, because the little significant bits are always in the same place.

Again, I don't have extensive understanding of hardware side, so I might be wrong.