Why does having abnormal blood pressure lead to impotence?

Many reasons. The drugs used: diuretics and beta blockers, etc. But remember, if you have other co-morbid conditions such as cholesterol issues, or diabetes, you may have vascular disease as well. Also, obesity in men converts testosterone to 17-b-estradiol, an estrogen. This is not good for libido. Remember, obesity can lead to all the above, and treatment can worsen it.