What do you mean you say a profession is valued less? Do you want to suggest that it's done deliberately by someone or something?

The value of each profession is always a reflection of the market, that is, supply and demand. The employee always wants to be paid more and the employer always wants to pay as little as possible (regardless of the employee's gender).

If women were universally valued less as employees, that would just create a massive opportunity for companies hiring only women to have margins greater than their competitors. In a short time, many other companies would seize the same opportunity, increasing the demand for women's labor and thus normalizing the wages across gender.

My speculative take on this is that the biological differences between genders reflect on their average personality traits, making them choose jobs differently.

For being more competitive, men tend to pursue high-income careers and positions. Also, men have a predilection for things instead of people, which is a driver for choosing STEM careers. On the other hand, women gravitate more toward the humanities and don't focus so much on increasing their income. Of course there are plenty of exceptions, but on average, this seems to be the case.