Smaller, 6-bit code pages existed before and after that. They did not even have space for upper and lower case letters, but had control characters. Those codes directly moved the paper, switched to next punch card or cut the punched tape on the receiving end, so you would want them if you ever had to send more than a single line of text (or a block of data), which most users did.

Even smaller 5-bit Baudot code had already had special characters to shift between two sets and discard the previous character. Murray code, used for typewriter-based devices, introduced CR and LF, so they were quite frequently needed in way more than few years.

Maybe 32 was a bit much, but even fitting a useful set of control characters into, say, 16, would be tricky for me. For example, ^S and ^Q are still useful when text is scrolling by too fast.

On top of the control symbols being useful, providing those symbols would have reduced the motivation for Unicode, right?

ASCII did us all the favor of hitting a good stopping point and leaving the “infinity” solution to the future.

I started using the separator symbols (file, group, record, unit separator, ascii 60-63 ... though mostly the last two) for CSV like data to store in a database. Not looking back!

only that would have broken the whole thing back in the days ;)

It is interesting that, as a guess, we waste an average of ~5% of storage capacity for text (12.5% of Unicode's first byte, but many languages regularly use higher bytes of course).

I don't fault the creators of ASCII - those control characters were probably needed at the time. The fault is ours for not moving on from the legacy technology. I think some non-ASCII/Unicode encodings did reuse the control character bytes. Why didn't Unicode implement that? I assume they were trying to be be compatible with some existing encodings, but couldn't they have chosen the encodings that made use of the control character code points?

If Unicode were to change it now (probably not happening, but imagine ...), what would they do with those 32 code points? We couldn't move other common characters over to them - those already have well-known, heavily used code points in Unicode and also iirc Unicode promises backward compability with prior versions.

There still are scripts and glyphs not in Unicode, but those are mostly quite rare and effectively would continue to waste the space. Is there some set of characters that would be used and be a good fit? Duplicate the most commonly used codepoints above 8 bits, as a form of compression? Duplicate combining characters? Have a contest? Make it a private area - I imagine we could do that anyway, because I doubt most systems interpret those bytes now.

Also, how much old data, which legitimately uses the ASCII control characters, would become unreadable?