I think it's true that the messaging in March and into April was that masks weren't likely to be effective. I remember the US Surgeon General tweeting that people don't need to be buying masks. At that time there was also concern that demand for masks from the general public would limit supplies at hospitals.
But in the meantime, new research has been coming to light evidencing that the virus transmitted though the air much more easily than first anticipated. The R0 values are higher than previously thought, and a number of airflow analysis reports and investigations of mass infections (e.g. at the bio-tech conference in Boston in February) have supported a revised view on the likely effectiveness of wearing a mask when around others . . . especially indoors. Also, we know that asymptomatic (or presymptomatic) infections are carrying sufficient viral load to be transmitting if the person is in public.
So we have a situation where mask supplies have increased and hospital need seems to be met. Contagiousness through the air is more potent than first believed.