This is correct and such systems do exist, sometimes combined with sources of ions and HEPA filters. However if you're already drawing air out of the room, it's easier to just filter it with HEPA than dealing with the additional complexity of UV lights (deterioration, energy consumption, replacement).

HEPA filters also have deterioration, energy consumption (pressure drop ain't free), and replacement.

HEPA is a mature technology with no big improvement curve, but UV treatment is seeing progress.