That's probably a form of supplier induced demand. As long as there will be lots of programmers willing to dedicate their whole day (and night) time to work, there is no reason for the employer to accept any extra-effort with uncertain extra-outcomes by following uncommon employment policies.

So unless a growing fraction of developers starts recognizing the benefits of part-time employment and start demanding it from their employers, it is unlikely that these change their policy for those reasons stated in the other posts.

I think this isn't a specific programmers issue. Most employments that are traditionally assigned to the male gender are full-time by definition. Because, traditionally, men care for the cash flow women care for the family. While women nowadays also claim a work-life, the male role model is yet a full-time work, spare-time private projects model.
So, up to now the emancipation of women came at cost of the family aspect of life.
Decreasing birth rates and increasing public child care tells a story.

The point of this, the emancipation of men, that will allow men to prefer family over the job, is the next step of the emancipation of women. This step _will_ follow, yet in question is _when?_
To relate back to part-time programmers: this is a matter of role models and society, and not a question of what extras the employers are willing to grant to their employees.

I think in a healthy society there will be an equilibrium state where both (or all, whatever) genders are equally doing a bit of work, and a bit of family, and a bit of private projects. Up to then, I recommend consulting [the Idler][1] by Tom Hodgkinson to everyone who has read this text so far.

  [1]: http://idler.co.uk/