They cannot charge you more for being morbidly obese, or riding motorcycles, out preexisting conditions, or anything at all but maybe smoking, so I’m not too worried about doneness.

Or who eat meat "too often".

I guess grilling vegetables is off the table, then?

The problem is that if the majority of people who use grill thermometers are using it for meat (probably true), and the health insurance's actuarial tables show that eating meat is associated with higher payouts, your premiums will go up. This isn'tat court of law. Even if you really did use it for grilling vegetables they won't care. As long as they're right in aggregate they'll continue doing it.