The original exemption, which dated back to the 1960's, only applied to people who worked in highly specialized wings of computer science. It was intended to exempt only the most advanced engineers, who were seen as being educationally and professionally equivalent to doctors and lawyers (my father in law, who holds three PhD's in computer science, aerospace engineering, and math, and who wrote software to augment primitive fly-by-wire systems for Grumman in the 1960's and 1970's and rocket guidance software for the Pentagon after that, was an example of the type of specialized workers they wanted to exempt).
In the early 1990's, Congress ordered the Department of Labor to expand their definition to include programmers, system analysts, and the like. The Department of Labor complied, but kept the requirement that they be specialized. Congress responded in 1996 by passing a law to override the Department of Labor's rules and allow just about any computer professional to be exempted. That change (predictably) came after years of lobbying and big campaign donations from the then-dominant powers in the computer world (IBM, Hewlett Packard, Microsoft, Sun Microsystems, etc.) That gave us the system we have today.
Even this wasn't enough, though. They tried to push the CPU Act through a couple of years ago, which would have relaxed the rules even further. The CPU Act would have relaxed the rules for anyone in an "information technology related occupation", including everyone from graphic artists to QA testers. Luckily, that one was beaten back.