That's an interesting point, but then one wonders that if software eng are ultimately artists, why are we not having them work on their portfolios like the other art disciplines? Is that the fundamental problem?
I think it's frowned upon in many circles because most of the work you do for a living cannot be released to the public, so there's an expectation that you will be cranking out work for free on the side just to build a portfolio, which is not inclusive for say.. a minority mother of three, who doesn't have the time, and it only favors young affluent white and Asian males with no dependents.
A lot of painting still life comes down being comfortable with brushes and knowing how paint works. A lot of music comes down to know scales and chords work. Most art still requires fundamental mechanics.
Who is having whom? Having a portfolio of work is a well understood benefit, and a lot of candidates have been doing it for some time.