In people with hypotension why doesn't their heart rate increase to compensate?

It should: Acute hypotension should trigger reflex tachycardia/ increased heart rate unless they take medicine to keep their heart rate under control or they have some other condition that will impair the reflex response. Some people live at lower blood pressures- in 2 digits and they do not have a reason to have tachycardia until their blood pressure falls from their baseline.