Producing a four-digit numbering format just took up too much memory. The two-digit format reduced resource consumption. Also, perhaps the makers assumed that the problem would eventually fix itself as a result of the increase in technology in new computers. But the focus of the Y2K problem today is less on reflecting about how the Y2K problem began as opposed to simply resolving this problem. I believe that paying attention to the source of the Y2K problem and heeding its lesson will separate the proactive companies from the reactive companies, and in turn may spell the difference between success and failure beyond the year 2000.
Proactive companies think ahead.
They take action before a problem occurs, and they anticipate conflicts before they have to deal with them. On the other hand, reactive companies solve problems as they occur. Also, reactive companies tend to assume that other people will solve their problems, therefore they won't have to. Obviously, the makers of the first computers had a reactive mindset, not thinking ahead to either a new century, or the new millennium. As the year 2000 rolls around, hopefully the number of companies taking a proactive approach to problems will increase.