Actually COVID is one of the most used tests they do, at least around here. But you can do things like drug use, cancer epidemiology (for some cancers), etc. as well - and that is incredibly helpful from a public health point of view.
Because it’s just like with Covid - we can’t get proper data from patient sided tests because we can’t test everyone. And even if we could,not everyone would.
But everybody poops/pees. And guys like OP interpolate from that.
Why not both? There are a fair bit of positions that allow a certain degree of patient sided work. And of course there is always Freelance/Locum work in most countries.
I have switched to a full off-patient role a long time ago and since the beginning of Covid I have worked mostly remotely. But I am still working as a Freelancer for a few shifts per month, depending on my workload.
And I like this model a lot.