As for the changing of recommendations regarding masks for the general public, the answer is not secret nor nefarious. The masks were in short supply and the healthcare workers with greatest exposure risk needed them. At the time COVID was not pandemic and the general population was not statistically at great risk. There was wide spread hoarding if you recall. I had N95s from my autobody paint use and these were donated to local hospital who had only a few dozen left.Fauci Explains Why We Didn't Wear Masks COVID-19 Began - TheStreet
When this situation shifted, both availability improved and the disease had spread justifying general population use, the directive changed. Was this done perfectly, nothing ever is.
Regarding the value of masks now we know the virus can spread via very small particles, this is near the bottom of the science article, read this article in full:
Once the mechanisms leading to airborne transmission are fully understood—acknowledging that transmission by aerosols is largest at close range—it becomes clear there is an overlap in precautions and mitigation measures for both droplets and aerosols (such as distancing and masks), but extra considerations must be taken into account for mitigating aerosol transmission at both short and long ranges. These include attention to ventilation, airflows, mask fit and type, air filtration, and UV disinfection, as well as distinguishing measures between indoor and outdoor environments. Although our knowledge is still increasing, enough is already known to add protective measures to better protect against airborne transmission of respiratory viruses, noting that “droplet precautions” are not replaced but instead expanded.