What is it about a person leading a relationship?

I hear that most relationships /marriages are "Lead" by men and I also hear "Female lead" relationships

Now I might be dumb , but I never understood it

Relationship is about partnership and why is it that one person should "Lead" and other should follow?

Why can't it be both of them equally communicating , arriving at a conclusion and moving together?

What is it about a person leading a relationship?
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