Wu Zetian raised Toy Boy mainly because of power. After all, it is normal for an emperor to have three palaces and six courtyards. You can't blame her just because she is a woman. Why can men and women not? As long as you have the power, you can do whatever you want. When Wu Zetian cited Toy Boy, the whole court knew about it, but no one dared to say anything, because they knew that if they said one more word, they would face the charge of decapitation.
And those Toy Boy also want to be with Wu Zetian, because Wu Zetian can bring them endless benefits. Under the protection of Wu Zetian, they can do whatever they want and have unlimited power. Although it may not be so rampant in crowded places, as long as no one is around, these Toy Boy will reveal their true nature. They don't really like Wu Zetian, nor for her beautiful appearance.
Just to seek temporary stability for myself. Wu Zetian also knew that she was old and faded, so she could only use her power to make deals with these Toy Boy people. Wu Zetian also longed for someone to accompany her, and someone to talk to her when she was sad. So she didn't maintain the secret book, only the power.