also because infectious diseases became less common thanks to vaccines and because antibiotics lowered the risk of spreading infection. (treated TB stops being infectious within a week, for example.
part of it was that the “experts” started pooh poohing all those old fashioned treatments used for years by ordinary docs: they didn't approve unless they passed a test.
Some UV tests showed they helped, but others showed they didn't help since you caught the disease anyway outside of the area where the light was shining.
A friend of mine and I, both retired engineers, have begun a for fun study of using UV to tread air in HVAC systems. The systems are commercially available. Honeywell make some of them. The question is how effective are they? How much intensity and residence time is required to be effective?
Some people, new kids on the block usually, have to make a splash to change things when they don’t know why they are there in the first place. There are other ways to apply UV than by direct exposure. It depends on what you are trying to prevent.
Some of the infectious diseases we dealt with and subdued have revived. Nothing stays the same. Maybe some old ideas need to come back. The amount of infection in hospitals now just feels unrealistic and unnecessary.