1. I haven't seen that idea claimed anywhere. 'Most','very many'???
2. There was a great shortage of N95s for hospitals for a long time. (Let alone 'nursing'-home death-traps, where 33% of US deaths - 179,000 - have occurred. [0]) Sterilization methods took months to emerge.
3. Consider how dense viruses get in IC units, compared to retail locations.
I saw an article the other day saying they'd given the FFP3 (out N95 equivalent) masks to the nurses in the ICU where patients are on ventilators, but the nurses dealing with the less sick patients just had surgical masks. Unfortunately, the less sick ones were up and about, coughing everywhere, not connected to machines to regulate their breathing and so those coughs are going into the air. Sadly lots of NHS staff have died.
Most of the very many dead healthcare professionals were wearing N95s that had been properly fitted.