This paper points out the filtration of SARS-CoV-2 isn't clear cut whatsoever. Papers stating it could be filtered from the air all demonstrated to have publication bias. The thing about viruses is they are super tiny. On average, a virus is 10x smaller than a bacterial cell. This makes filtration much more difficult to accomplish.

The study found the most effective methods for air purification were germicidal lights, ionisers, and electrostatic cleaners. With HEPA specifically, the filters can snag objects as small as 0.3μm. However, the largest viruses are 500nm or 0.5μm in diameter. Based on the numbers, HEPA filtration is capable of removing the largest viruses from the air, but that's a small minority of all viruses. SARS-CoV-2 comes in somewhere between 60nm/0.06μm to 140nm/0.14μm in diameter, meaning HEPA filtration can not remove it from the air.

That’s what I was wondering. Like not that it can’t work but that it wasn’t implemented at the sufficient scale to do what it is purported to do.