...
Sigh.
They aren't even a "de facto" standard when they are only used by Atari, Commodore, and Sega... are you aware of how many different game systems and computers were available at that point in time?
The fact that Commodore and Sega (sort of) used Atari-style joysticks and connectors doesn't make it a defacto standard when Apple, Texas Instruments, IBM, Coleco, Intellivision, Radio Shack/Tandy, Timex/Sinclair, and many others all used DIFFERENT connectors and joysticks... not to mention Nintendo.
I'll grant that there was a period in time in which the Atari-styled joysticks were the best selling overall, but the computer/game market of the early 80s was fragmented enough that there was no joystick standard (real or de facto) of any sort.