Why does having labnormal blood pressure lead to impotence?

Atherosclerosis. High blood pressure is a risk factor for atherosclerosis which can interfere with genital circulation and lead to erectile dysfunction. Diabetes, smoking and high cholesterol compound the damage. There are other causes of ED though too so it should be investigated.

Related Questions

Wanted to know if taking blood pressure drugs can cause impotence?

Yes. Some of the various blood pressure meds can cause impotence as well as antidepressants. One hypertensive med that can do this is beta blockers. You should see your doctor for advice. Review all meds you take that you know to make sure no other med is causing or contributing to this.
Yes. Depending on the drug but a more common thing is that decrease libido. A trip to the doctor and a discussion will help sort it out.