Historical revolutions, like Iran's in 1979, are not clear-cut events with a predetermined winner. For years, they exist in a state of flux with multiple factions competing for control. The eventual outcome is only obvious in hindsight, not to those living through the uncertainty.
It doesn't take a majority of a population to enact significant political change; a small but sufficiently fervent and motivated minority can be incredibly effective. Their passion and commitment can outweigh the apathy of the larger population, similar to the low engagement rates in modern political parties.
The Iranian Revolution's significant impact on American public opinion was fueled by its visual foreignness. Images of bearded men, austere clerics, and frenzied crowds created a sense of "otherness" that was deeply unsettling to a Western audience unfamiliar with the religious fervor driving the movement.
In the late 20th century, the prevalence of black and white news photography was driven by practical constraints. Black and white film could be quickly developed in makeshift darkrooms, like a hotel bathroom, and there was no commercial demand for color images as most newspapers did not yet print in color.
Top photojournalists like Abbas Atar operate beyond the daily grind of selling images to news outlets. They are often driven by lifelong, thematic passion projects. Abbas, for instance, spent his career documenting the effect of religion on societies, including a seven-year project on jihadism post-9/11.