Just for conversation's sake: That's largely because you're still sitting on a pile of legacy cables, and manufacturers are (often) still equipping their devices with legacy ports and including legacy cables.
Until a person transitions, it's always going to be "easier" to stick with what they have.
Much easier to transition now than it was 2-3 years ago. For an HDMI TV or monitor, a simple
$15 USBC/HDMI cable gets the job done. Similar cables are readily available for displayport. Various cables to connect USBC to USB3 micro or USB2 micro (or mini) are readily available as well in the $7 range on Amazon. Type A to type C adapters to convert existing cables
are as low as ~$2.50 each.
We've done this before: Why aren't the forums filled with people clamoring for VGA ports, DVI ports, DB9 serial ports, PS/2 keyboard & mouse ports, or even parallel printer ports? Because we've transitioned away from them -- or folks entered the market after they'd gone the way of floppy disks. *During* the transition though, people did need to adapt/adjust. Even with USB, we had a bit of a transition from the typeB connector to type B mini and finally to type B micro.
Let's also not forget the cries of doom when Apple dropped optical drives...