Apparently because scientists think men won't take it. According to an article in Science Progress, outdated ideas of who's responsibility birth control and contraception is, has put the burden on women's shoulders.
Let's pretend you are a straight couple, in a monogamous long-term relationship, and you don't want a kid. Consider your options: A woman can choose from 11 forms of contraception -- including barrier methods like the diaphragm, permanent sterilization, and that holy grail of the sexual revolution, the pill, and its more recent and even more foolproof sisters in hormonal birth control, the ring and injectibles. A man can choose two: condoms or a vasectomy.
Right, so according to science, if you are woman it is your problem if you get pregnant or end up with an STD, so it just makes sense if you take care of the birth control. Doesn't sound very scientific does it. Furthermore, the financial burden, time constraints and side effects of hormonal birth control on women has another implication on not only time, but unfair burden.
Not being responsible for some or all of these economic, health-related, and other burdens is a significant boon for men. Men typically do not have to dedicate time and energy to contraceptive care, pay out of pocket for the usually expensive and sometimes frequent (often monthly, or at least four times a year) supply of contraceptives, acquire the knowledge about contraception and reproduction needed to effectively contracept, deal with the medicalization of one's reproductive health, endure the bodily invasion of contraception, suffer the health-related side effects and the mental stress of being responsible for contraception, and face the social repercussions of their contraceptive decisions (such as whether to use a particular contraceptive or to switch contraceptives), and the moral reproach for contraceptive failures.What both Lisa Campo-Engelstein from Science Progress and Amy Benfer at Broadsheet acknowledge is that this outdated ideology not only leads to the false belief that men wouldn't take contraception, but also leads to a disempowerment of men taking responsibility for contraception. As in, they benefit from the structural belief that it is a woman's responsibility and it is a lose-lose all around. To counter that narrative would take a leap of faith on behalf of women and an insistence by the science community around the effectiveness of male birth control and the corresponding research, development and distribution of such measures. So, it is possible, but sex education, the science community and health care providers would have to overcome the sexism endemic in the way we teach and distribute contraception.