FDA doesn't get paid for this.
The issue is that nobody has made a reliable blood monitor. Not even close.
I mean, check the oxygen sensor, mine regularly drops to 88% on my watch, but is never below 98% when I go to the doctor.
Not sure what you mean by 'this', but the FDA absolutely gets paid for evaluating products for approval. For example the 2023 fee for a BLA, Biologic Licensing Application, is $441, 547. And while the FDA is an organization, it is comprised of people that get paid by the government to review products for approval. It is literally their job. So yes, they are charged with protecting the public from snake oil salesmen, but its erroneous to say they don't get paid.
Now you bring up the Apple Watch Oxygen sensor. Great analogy. Apple takes great efforts to say their O2 sensor and their Heart Rate sensor are NOT FDA approved. They do not advertise it as such, or the FDA would be down their throats and report them to the SEC. But they do sell watches with those capabilities. And you are right, they are not as accurate as medical grade devices, but by and large if you learn to disregard outliers the trends are reasonably close so as to be useful. The trick is to take several measurements in a row.
So I assume that if they come up with a glucose monitor, probably by monitoring glucose glycosolation of hemoglobin resulting in a very slight spectral shift as compared to the huge spectral shift hemoglobin undergoes when binding oxygen (red) and being dexoxy (purple), Apple will be clear in their marketing this is not FDA approved.
The interesting thing to me is the FDA DID clear the two functions on the Apple Watch, which is very different from marketing approval... and yet they take this very anti-stance about glucose monitoring. They didnt take this stance before with the Apple Watch. The FDA is a very reactive organization, so my guess is they regret they let the genie out of the bottle with the heart rate monitoring feature even though it is more benign. My grandfather was a diabetic, and we had to measure his glucose before dosing him with his meds. My guess is that is what has the FDA scared, especially when they see the widespread adoptance of the Apple Watch health features by the public AND doctors, that people will trust their watches too much.