America is a flawed democracy but is there really no hope for it to change?

I see much despair from Americans often about various things but to me as someone from an authoritarian conservative country, I really don't understand it.
Didn't you guys abolish segregation laws, gave women the right to vote (and the vote actually counts many authoritarian countries today allow women to vote to appear civilized when it doesn't matter at all), gave women the right to financially independence, gave gay people not only the right to exist but also the right to marry, and more all in the span of a century?

The American society changed significantly, and I don't see why it wouldn't change more for the better in the upcoming decades.