> All of this is try for multi-level electronics but even more so, making it easier and more reliable to work in binary than 3, 4, or more levels per bit.
You don't need many levels. IBM's tabulators used pulses to represent numbers in decimal (e.g. 6 pulses to transmit digit 6). That's why it is surprising that computer developers didn't reuse existing technology and went with a new system.
Above certain speeds, pulses based systems have timing issues. How many pulses can you cram in before they start to merge due to signal noise? Assuming serial communication transmitting 9 pulses is more than the 4 needed to represent 9 in binary (assuming 0 is represented by no pulse, not a single pulse with no signal at all indicating an error condition). If you allow variable length transmissions pure pulses become more efficient overall, but synchronising multiple signals potentially becomes more difficult.
So you fix the signal merging issue found in multi-level signals, but introduce other similar difficulties. Both sets of issues get more problematic as signalling speed increases.
You don't need many levels. IBM's tabulators used pulses to represent numbers in decimal (e.g. 6 pulses to transmit digit 6). That's why it is surprising that computer developers didn't reuse existing technology and went with a new system.