Why don't we use the same connector for all digital signals?
There are a couple of reasons, but I think one of the big ones is the speed of the various signals. Take, for example, USB 2.0 and USB 3.0:

Source: https://theydiffer.com/difference-between-usb-2-0-and-3-0-cables/
USB 3 adds those extra five pins at the top, which are used in SuperSpeed mode (total bandwidth of 5 Gbps, which is much faster than USB 2!) To carry such fast signals, you need higher-quality cables, which are more expensive. Designing circuits capable of such speeds is also more complex--you might need to go from a 2 layer to a 4 or 6 layer impedance-controlled circuit board, or you might need to use more expensive ICs.
There are many things that just don't need that extra speed (think of peripherals like a mouse or keyboard) and forcing everything to use one very high quality standard would just drive both prices and complexity up.
You can see this with the current mess that is the various types of USB Type-C cable. The different types of &quot;USB-C cable&quot; have different capabilities--some can only do USB 2.0 speeds, some support SuperSpeed, others support even faster standards like Thunderbolt, some support Power Delivery. You could just get the best, most capable cable for everything, but that gets very expensive very quickly.