Actually, I suspect that one of the main culprits is very simple: unless you're a hypochondriac or suffering from Munchausen's, you don't like being sick and you don't like taking pills. Taking a variety of pills for six months, especially pills like antibiotics, is miserable. Your gut flora suffers, and it wreaks havoc on vaginal flora as well. Who wants to keep putting up with a raging yeast infection for six months when they're already feeling better after two? Furthermore, who can afford to continue taking meds for six months? I have to say, even knowing full well the dangers and repercussions of such behavior, I would be hard-pressed to finish a 6-month course of antibiotics, especially strong ones. I don't think it's too far of a stretch.
And before people start plusone-ing my post and saying, "yeah, people are stupid! Victims of their own stupidity!" or something, I'm not saying that. It's not stupid not to want to be sick for six months from meds that you are voluntarily ingesting. It's very human, and evolutionarily wise: after all, previous to the introduction of antibiotics, voluntarily ingesting something for six months that made you feel ill would not have been a wise move, evolutionarily speaking. It's just... people are people, everywhere.