Many reasons. Survival and safety being one. In unsafe environments (the hood, abusive homes, warzones), adopting aggression, confidence, and toughness is protective.

Vulnerability can be exploited, so women learn to mirror the behaviors that command fear or respect.

If you're in the hood, women have to be as violent as men for survival. You know how many young women end up dead in the alley?

I saw something on cctv once where a male approached a female at a bus stop. He tried to kidnap her in broad daylight, she gets out her gun while he was grabbing her. You could tell the guy def. had his life flashed before his eyes. If she wasn't aggressive, how do you think that would have ended?

Another one is power dynamics. In societies dominated by male power structures (machismo cultures or patriarchal systems generally), traditionally “feminine” traits like gentleness or submission are undervalued, while “masculine” traits are rewarded.

Women adopt them to gain respect, authority, or basic autonomy.

Another reason, economic survival. In many jobs or industries, women have to act in ways coded as “masculine” (decisiveness, directness, assertiveness) to succeed or even be heard.

Another reason are cultural shifts. Modern feminism and gender theory have challenged rigid gender roles. Many women no longer see femininity and masculinity as binaries but as tools or traits anyone can use.

Gender is fluid, these traits aren’t owned by one gender.

Another reason may be psychological adaptation. If a woman grew up in environments with male siblings, absent nurturing adults, or abusive situations, adopting “male” behaviors can become an internalized survival strategy.

Also, social learning and trauma. Many women experience sexual harassment or assault early in life, leading them to toughen their demeanor to protect themselves.

It's a multi issue with no one cause but at the root of it are those issues