This question has been addressed numerous times even recently. You might want to search the threads. Not as many nations adopted it = less parts to build clones with, Also less countries that actually tooled up to make them and or stopped making them so to produce would have to retool for it. AR platform are cheap in comparison makes it hard to justify investing to produce quality parts to a market that may be very limited and where potentially an AR might run $300-600, partial kits minus reciever and barrel were running about $450 or more before dried up, kits with barrel are running $800-850 right now if you can find them.
THEN you have the problem that hardcore HK fans want an actual HK93, full auto guys will allow for a clone if built with quality HK or contract parts because they do not want to wear out their actual HK rifle. After that you are left with a very small market of HK fans who will buy a 93 clone because they want an example of one but are not in the position to shell out the funds for the real deal.
And of course there is the Century debacle.