it might be better but it isn't mainstream just yet.
how many usb flash drives or external hard drives that people own or that are on sale now come with USB-type C and standard?
you cant just go cold turkey and ditch one port and put another and expect people to adapt overnight.
you have to phase it out.
maybe have 1 usb 3.0 port at least so people still have time to ditch their current hardware for the newer one and give drive manufacturers time to start rolling out USB-C drives and phase out USB 3.0 hard drives.

and using adapters from USB to USB-C is just a waste of money because your speeds will never be as fast as USB-C standard. its like getting a VGA to HDMI converter, it will work but it wont be full HD. speaking of TVs, even they didnt ditch it for HDMI ports only and still have the analog aerial jack at the back.