To elaborate: Why must a USB cable look different from an HDMI cable? Why must we have B-type and C-type chargers? Why use circular audio jacks when it can be “USB’ed” instead? and so on
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In short, money. An HDMI cable has 5 twisted pairs, 4 solo wires, and 1 drain wire. That’s 15 wires to get the job done. CAT Ethernet cables typically have 8 depending on various things. A USB has 4. And an audio jack (without mic) has only 3. Why would you pay for a more expensive cable than you need? So the next question is, could we standardize the plug and have a bunch of different options for how many wires run between them. People have tried that. Back 15-20 years ago, serial ports (actually called DF-9) we’re king. 9 pins, but as few as 3 might actually be used depending on the application. It was fairly widely used, but there are some other issues that toppled it. It was a lot bulkier than modern plugs, and connectors are still a big portion of the cost of a cable, especially shorter cables. Also, more pessimistically, if you make your connectors unique or just choose rare or weird existing ones *cough *Apple* then people will be forced to come to you for the accessories too. More money
Lastly, different plugs and wire configurations are good at different things. Remember above when I said 5 twisted pairs? Twisted pairs are commonly used for noise rejection. Most applicable when running digital data through a cable. Analog data can be more resilient to noise, mostly because if 1μs of a song comes out kinda funky, who cares? But signal quality is still very important. Reflections and distortions can happen at connectors especially because the impedance can change drastically compared to the wire it was just running through. So your typical 8mm or 16mm aux jacks are specifically designed for audio signals (20-20,000 HZ). Higher frequencies are often used to carry additional data like in cable internet. Coax cables with BNC connectors do a better job of reducing reflections in up to several MHz transmissions. In fact, BNC connectors are often sold by resistance in Ohms. You need to know what the impedance of your source and load look like, then use the right resistance connector to match them as close as possible to avoid reflections.
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