Do they not worry about getting infected? Are they not aware that they too might be spreading disease?

A sex addict in a rough spot will have no problem paying the scariest looking drug-addicted grimey scab-covered woman for her time. I doubt COVID would scare him away, STDs are only a faint concern shoved way down into the noise of the loud appealing addictive voice.

Only afterwards will he see clearly who he just had relations with and he'll think "how could I have done something like that" and he'll be as outraged at himself as you are, as a normal healthy person would be. Then the shame and disgust build up and the cycle starts over again.