The requirements for responsible code are very different for Yahoo Shopping and Ultima Online and Word 2020. I might have to live with periodic bugs and outages in my free online Fantasy Baseball team, but not in my pacemaker. How do you even begin to come up with licensing programs that deal with the diversity of the software world?
What about the open source world? Lots of projects have no central authority, and no real place for a 'licensed programmer'. Not to mention being hideously international. How could you begin to enforce any of this?
And practically, it'd throw a monkey wrench into the economy of small companies. Many commercial projects are just two or three people. Licensed Programmers may make sense for big companies, but for startups, they could drive up costs and create artificial barriers to entry. It's hard enough getting a software company off the ground as is.
There may be virtues to having the concept of a programming license, but the practical realities are very difficult to solve, and I think that it's far from inevitable. Companies don't want it, programmers don't want it, and consumers don't want it - at least, not in large numbers yet.