Because girls aren't interested in a bum who collects social benefits and doesn't work. This incentive will never change.
It really depends on what you mean by "work". I've had a relationship go down the drain, largely because of work that took too much of my time and energy. At some point I decided I'm not going to let work ruin my life again. I now pursue my own thing in art and science -- with a journal article and a conference talk coming up, I guess I'm doing something right. The girls don't seem to mind all the fun and interesting projects I'm doing instead of a soul-crushing day job.
Personal stuff aside, a discussion such as this should get its definitions right. Most people are doing all kinds of interesting and useful things all the time, but outside of a defined "work" -- think open source software, for example. Or raising children. It's more or less arbitrary which part of this great human thing goes under the "work" umbrella, which I define by getting paid for it. Traditional economic theories only seem to care about things that involve money, ignoring the big picture altogether. This is exemplified in the following bit of the article.
- Shorten working hours, bringing supply down to meet demand, and improving the quality of life by providing more leisure time.
- Invent—or import—new things for people to buy that will improve their quality of life.
To me, having to choose between these seems rather silly. My general idea of life is to get more leisure time, in order to do/invent fun things for me and others to enjoy. "Work" with its schedules and bureaucracies just isn't very compatible with my creative wants. Besides, I'd expect real communists to ditch this idea of money/buying/selling for good.