WP8.x OS is not built for user installable driver installations. Drivers must be pre-loaded in the firmware.
There is no common industry standard for printing generically unless all you want is just plain unformatted text output (like back in '80s).
Apple introduced an Apple proprietary AirPrint protocol which works only with Apple products and expect printer makers to support such protocol in printers. As it goes, anything Apple introduces, device makers will support.
Microsoft has no such market force, nor did it introduced any such mobile printing protocol.
Yes, it is an oversight but even if Microsoft introduced it today, I suspect no printer makers will introduce any printer to support it within couple years. And don't expect your existing printers to ever support it.
EDIT: actually, Microsoft introduced XPS printing back in Windows 7 Desktop OS days and expected printer makers to embrace it but I have not seen anyone made any printer that supports XPS printing. So, I can understand why Microsoft doesn't want to include it in WP OS.