That shorts together a lot of the contacts as you're plugging it in.
There are of course various devices which somehow ended up using TRRS for USB, but unplugging/plugging those while powered is definitely not recommended:
Most of this is just cheap design on part of the ergomech community. It's not that hard to add some protection. E.g. some keyboards use a Schottky diode on VCC for reverse polarity protection and ESD protection diodes to protect the data lines:
Of course the design requirements of USB would be different, since you'd always plug/yank the cable on a machine that is on, rather than protect against doing this accidentally sometime. Given that, it probably made more sense to completely avoid the issue.
It's more an issue of ESD protection being kinda tricky on DIY boards due to the need to stick with THT parts. When you're building a $200-$300 keeb, a $0.05 diode doesn't really all that much price-wise.
ESD protection diodes also don't really solve the problem. They are intended for short-duration high-voltage low-current spikes, not long-duration low-voltage high-current ones. Definitely better than nothing, though!
I'm not an expert but couldn't you just make the tip live and not connect the rest until that's connected? Or have a switch for when the plug is fully inserted. I see that it's a problem for sure, but it seems easier than the problems they solved to make usb c reversible
> I'm not an expert but couldn't you just make the tip live and not connect the rest until that's connected?
No. You have to deal with disconnects being possible at both the host side and the device side. Making the tip live means you're touching a live wire to each contact in turn while plugging in the device side.
They'd have to make it not fit in a normal TRRS hole or use some fancy power negotiation stuff to avoid blowing up headphones. It would be cool though. But perhaps easier to mess up than USB. Cheap headphone cables aren't great.
TR/TRRS have very small contact patches since you're connecting to the tangent of a circle. That's not good for anything carrying more than a very small current. And even then, it can be an unreliable contact.
