It's easy to say "just diet ez" and it's hard to "just diet".

If you can administer a treatment as a simple one and done thing, that's alright. If it's a pill you got to take every day, that's pretty bad. More than once a day? Horrible. Why? Because a lot of patients just don't have it in them to take a pill 3 times a day consistently.

If it's purely an "exercise willpower" thing or a "change your lifestyle" thing? You might as well give up.

The medical establishment wants to do things that work. Telling people "go diet" doesn't work. Semaglutide, evidently, does.

You say force a diet change on a patient. OP certainly meant forcing a diet change in the input of American factories. Sugar can be found in fruits. That's the right place. If you need some, use fruits, maybe alcohol. Everything else can be slashed. No sugar in prepared meals anymore. No sugar in pasta anymore. And most of all, no sugar in water. Sugar input makes more damage than cocaine today.

We can call it the Prohibition II. There will be underground bars with sick people binging on sugar. We can change the shape of sugar to prevent restaurants from adding it to food. We can make it bitter. Absolutely need sugar? Eat that lemon-tasting block. We can call it The War On Sugar.

The medical establishment that I have familiarity with (in the US) pretty much only ever treats symptoms, not causes.

Don't believe me? Next time you go to see your primary care physician, ask them what you should be doing to lower your risk of whatever malady tends to run in your family. (Diabetes, cancer, dementia, etc.) They're going to stare at you in blank confusion for a few seconds before making some vague suggestion about a better diet and more exercise. Guaranteed.

The reasons are many, and detailed enough to write MANY books about, but the low hanging fruit is: we don't have a culture of monitoring and improving our own individual health, physicians are trained almost exclusively to solve problems not prevent them, modern nutrition science is a joke, omnipresent health insurance distorts incentives for everyone, doctors are too overworked to get to know their patients, private equity has captured a large chunk of health care, drugs are positioned as the first line of treatment for almost everything, etc.