Why do men not take birth control?

Because it is not in the market. Nor would it be desirable if it were due to how it works.

The only way birth control works for men is to reduce their testosterone levels, which in turn reduces sperm count. However, that makes them fat, cranky, unable to get an erection, weak and suffer from other signs of low testosterone levels. It would also have a negative impact on the development of adolescent males and young males because adolescent males take it and enter the water supply. In summary, we know how a male contraceptive pill would work and we have even tested it, but it will not reach the market due to its functioning.

In addition, the pill is likely to reduce birth rates to around 0.5, which makes it quite detrimental to the global economy. As it is now, the female contraceptive pill is reducing birth rates to a point where it is harming the economy, so there is little reason to make the situation worse with a male equivalent.