I’ve followed the protests to some degree. The short answer: they lost, because the authorities had loyal goons and those had weapons.

https://en.wikipedia.org/wiki/Mahsa_Amini_protests

Key points:

By February 2023, the regime stated it had arrested tens of thousands of protesters.[49]

According to France 24, by mid-March 2023 protests “had dwindled” across most of the country.[15] On March 13, the government claimed it had pardoned 22,000 citizens arrested for protesting.[49]

Perhaps a staggering level of peaceful solidarity action would have helped, but in the end, if cops and other enforcers cannot be stopped with persuasion, shaming or other forms of social pressure, if they remain willing to use violence… then only more effective violence will stop them. :(

Before Iran, we saw that in Belarus in 2020, where mass rallies were beaten down and suspected leaders arrested or driven into emigration. Street protesters fought back using crude and limited self-defense tools, not enough to counter a modern repressive apparatus:

1,373 injured including children[57]

4–11 dead[58]

30,000+ arrested[59][60][61]

at least 6 are missing[62][63]

Before Belarus, we saw Ukraine in 2014, where protesters did overcome the police, but not before they started using tractors, shotguns and hunting rifles, firebombs to burn vehicles or firehoses to make their own water cannon. Cops no longer showed up to work - because work was becoming personally and incredibly dangerous - they were fewer than in other countries, there still existed a democratically elected parliament (to sort out the aftermath)… protesters made a great effort and deposed the president. The military was not political and stood down, letting events unfold (not the case in Iran or Belarus, not the case in Myanmar, etc). Chaos was short-lived, the parliament did sort things out. But then another country intervened in an unexpected way…

…the conclusion of rather depressing. Most successful revolutions require at least a bit of remaining democracy in the background, and an apolitical military. Even then, peaceful revolutions are rare.