As I understand it hashing is a new theory to programming databases. Almost all computer science majors going through school now learn the newer computer languages that are emerging like python and ruby (depending on application) and legacy languages such as C. The reason they teach the legacy languages is because a large amount of big business, even with its substantial capital can not afford to rewrite all of its software that was written a decade ago or in some cases even further.

A large team would have to be assembled in most cases of programmers who's base rate is 100-200 an hour to rewrite and rework existing code and patch it into a new or existing system. Your cost to do this for a large company is in the millions of dollars. If not hundreds of millions or billions.

Which is why some big box stores such as the big blue electronics box and the big red retail box's internal inventory management systems have been dos or command prompt applications for decades. Those are the only two I have direct experience with. They may or may not have changed in the last decade.