Probably because after she ran for her first term in the House in 1988 for the 101st Congress, there were only 29 women in the House and 2 in the Senate. She had run for the seat previously held by another woman who finished the term of her husband, one of Pelosi's friends, and had won 2 more terms before deciding not to run again.
When she was elected SOH for the 110th Congress almost 20 years later after the 2006 Democratic party rout, there were 72 women in the House and 16 in the Senate.
As of the 2024 election, in the 119th Congress, there are now 125 women in the House and 26 in the Senate.
To quote the old Virginia Slims ad - "You've come a long way baby".
And although today that ad would be considered sexist, there was a good write-up by the-now almost-defunct VOA in 2016 talking about what was going on back in the late '60s and recent politics - You've Come a Long Way, Baby. But It's Still a Man's Game
So given how much Congress has been "an institution by men, for men", one would naturally look more at the general populace itself for elevation of women in politics, given the demographics being more diverse there than in Congress (where the SOH is directly elected by members of Congress and not the general populace).
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