Why does a woman interrupt a man’s prayer?

Firstly: 

The Muslim has to accept the rulings of
sharee’ah, whether he understands the reasons behind them or not. 

Secondly: 

Women are not impure (naajis), but some of
the scholars said that the reason why a woman interrupts the prayer is that women are a temptation for men.  

Thirdly: 

There is a saheeh hadeeth in which the
Messenger of Allaah (peace and blessings of Allaah be upon him) said that these three interrupt prayer if they pass in front of a praying man
if he has not placed an object to serve as a sutrah [screen], or if they pass between him and his sutrah. ( See question no.
3404 ) . So we must accept and submit to the rulings of Allaah, and follow them. What is
meant by interrupting the prayer is that the prayer is rendered invalid, according to the more correct of the two scholarly opinions. 

And Allaah is the Source of strength. 

Al-Lajnah al-Daa’imah li’l-Buhooth
al-‘Ilmiyyah wa’l-Ifta’, 17/12.