-w, --wrap=COLS
wrap encoded lines after COLS character (default 76). Use 0 to disable line wrapping
The purpose of base64 is to turn binary into text that can be embedded in normal text messages such as email and Usenet. A right margin of about 80 characters is very much what one should expect such a tool to default to.
The primary purpose of these tools have changed over time as the environment has changed. You know nobody uses usenet anymore, and nobody copypastes base64 into emails anymore, right?
Also look into the text files für the public/private keys. It is always this, because the screen has only 80 characters in width.
- base64 is a stupid easy command to use the default behavior (guessing is easily possible)
- they probably would not have retained flags from the man page unless they needed to use them the first time they used base64
- they probably didn't need to use any flags with base64 in the past
- it's perfectly reasonable to expect base64 to base64 long inputs the same way it encodes short ones. In fact I would say any other suggestion is unreasonable
- it is perfectly reasonable to not read the man page again when you have a concrete expectation of how a program should behave