While there may not be a specific "ding" for being obese in most employer health insurance plans, the cost to the employer is based on the numbers that actuaries arrive at based on the average age of employees, place they live, and the health numbers in that area. And, those things do, at least to some extent, take into account a premium for obesity although it is indirect.
And, the difference is that obese people are basically only hurting themselves. Obesity isn't "contagious" and while the COVID vaccines don't totally stop people from getting COVID, they do reduce the risk of getting COVID by a pretty significant amount. And, from an insurance company perspective, a vaccinated person is far less likely to require a lot of costly medical treatment and hospital stays compared to a vaccinated person.
I mean, insurance rates are too high, but that's based on a lot of factors that really have nothing to do with how they decide who is in a higher risk group or not and is beyond the topic of this thread, but I don't see an issue with an insurance company setting prices based on how much risk they think a person has for costly medical procedures. And, frankly, that may include obesity in addition to being unvaccinated for any number of diseases.