The first computers DOS ran on were from a different era. The first PC model had 16kb of memory and a 160kb floppy drive. There was literally no space for error messages.

DOS itself literally took up an entire disk. You'd have a DOS disk with the DOS utilities like fdisk.exe and format.exe, but you'd boot off that, then swap to a program disk to do actual stuff.

One early DOS IDE (Turbo Pascal 2 or 3 I think?) would prompt you to load error messages off disk at startup. If you chose not to, it would free up some memory for your project and you'd need to look up the messages in the manual by error number.

Only a few years later, every PC had a hard drive, >1MB storage on a floppy, and the full 1MB real mode address space filled with RAM.

IIRC "The Design of Everyday Things" makes a point that most devices have poorly explained errors (beeps, error codes etc) because nobody chooses what to buy based on how it acts when it's failing, so there's no incentive to spend money on it. For hardware, the cost is quite literal, as having a better display just to show error messages is a lot more expensive than a beeper.

With software, it's probably a matter of prioritization, why invest into explaining errors when you can work on preventing them? Not that this error prevention always works out, but still.