Covid: Masks upgrade cuts infection risk, research finds

> In the weeks following this move, the rate of infections among healthcare workers on red wards dropped spectacularly, quickly falling to the level experienced by staff on green wards where there were no Covid patients

Why has taken so long to identify what type of masks are effective? Why did nobody do a randomized controlled trial of these FFP3 masks when the pandemic hit?

I find it strange that it has taken so long, given the simplicity of the technology and the huge potential benefit. How many lives could have been saved if this report was published a year ago?