When I point an (un)packing program at a packed archive, the default action should be to fucking unpack it.
And when I point it at anything else, it should pack it into the default format.
The problem is, tar isn't a packing program, it's a tape archive program that's been repurposed for general files-to-file archival with optional compression plugins
At this point, if it were written today, it probably would behave as you suggest, but changing it now would break too many things that use it
Then it would've been time to deprecate it for this purpose, and use something sensible instead, say about 13 years ago.
All the old stuff can then keep using tar, but the nicer option can become the standard for user-friendly file extraction.
"long-standing conventions" is how you end up with Internet Explorer still pre-installed on Windows Server 2025.
And when was the last time you used the tar "tape archiver" to archive things on tape?
Magnetic tapes are still being used as long-term storage, as backups for example. They are inexpensive, compact, have zero moving parts, and are more durable than optical media. All you have to do is keep them in a location that is around room temperature, relatively dry, and away from magnets.
But that's not really what tar does. It simply collects the input files and writes them to a single contiguous data stream -- a file not unlike an actual tape. It's worked like that for, I shit you not, 45 years, and it is very much a single project holding up modern technology situation. I fear to imagine what would happen if it were to change.
No human rights are violated by tar functioning the way it does, but changing it would cause a lot of problems without good reason since you could just as easily write an alias or wrapper to simplify the usage