Why should perimenopausal women not take menopausal hormone therapy?

Shouldn't?: In general there's no over-ruling reason they shouldn't take it, but ask instead what's the reason for them to take it? Often there may be other more suitable forms of treatment. Ther are of course specific reasons why an individual women might be cautioned against hrt.

Perimenopause: is the months before the cessation of menses. Many women have adequate estrogen during these months. Most women do not ovulate or ovulate sporadically during this transition so they do not produce progesterone. A blood test can determine your need.