Because you don't need a penis to float around in heaven, but you do need one to pass microphones around here on Earth. A woman cannot be expected to carry around a microphone phallic symbol while she menstruates and cries. duh.
The Scriptural position might be said also to take into consideration woman's biological nature. As every woman in the prime of life is well aware, she has certain difficult days each month during which she cannot give of her best and during which she very much appreciates her husband's showing her consideration. But if she had responsibilities of oversight and was required to hold forth regularly on the public platform regardless, either her performance or her health would suffer.