There are a lot of vegetables, whole grains, and beans. You can make an excellent diet just from those.

Small amounts of any of those "bad" things is just fine. The problem is that many people have come to see them as the core of their diet, with vegetables as an unpleasant supplement to be minimized. Learn to cook vegetables well, and vast frontiers of interesting, delicious food open up.

Indian food is an excellent starting point[1], for either vegetarian or vegan eating. For that matter most authentic Asian cuisines are heavy on the vegetables, with small amounts of meat for flavor, which is also a very healthy way to eat (especially if you substitute whole grains for the white rice).

Plenty of other cultures have thrived on vegetable-based diets. It's really not that difficult. You just need to get over the notion that "food" consists of a meat main dish, a starch, and a desultory, obligatory vegetable side.

[1] https://www.priyakrishna.me/indianish is a current favorite of mine.

The problem, generally, is that people are accustomed to certain tastes, and often "healthy" options are overloaded with things to make them taste good. Mayo on salads, tenderstem broccoli roasted with olive oil, corn cobs on a BBQ, etc. - and Indian food, at least as it's known in the West, is no exception. Curries tend to use a lot of ghee or oil, and I'm fairly sure that people skimping on the fat at home is why home recipes (usually from health-conscious/vegetarian/vegan recipe sites) never quite hit the mark. Vegetables can taste great! ...So long as you smother them with the junk that actually gives it the flavor and texture you like.

Think of a dish composed mainly of "vegetables, whole grains, and beans" with minimal carbs and even more minimal butter/oil. What is the recipe? Then, consider if it tastes good - as good or better than similar recipes where more carbs and oil is used. I've been cooking a variety of meat and vegetarian dishes of various cuisines for years and I know of no such dish I'd want to eat with regularity. Brown rice, steamed chicken breast, and cauliflower just doesn't cut it for my palette, and I suspect the same for the majority of people who know how good a Sunday roast or pizza tastes.

There's nothing wrong with a dish containing a fair bit of fats. A lot of plans call for getting 30% of your calories from fat, which is about 12% of food by mass (since fats are about twice as calorie-dense as carbs or proteins).

Controlling total calories is important in weight loss, and that's a matter of portion control. A diet with a good proportion of fat will be fairly satisfying; you just need to limit the total amount of it. That'll still leave you a little hungry. There's no magic that makes calorie deficit pleasant. Tweaking the ratios can make it less unpleasant, a matter of personal taste.

It doesn't need to be junk. You don't even necesarily need a calorie deficit, if you're happy with your weight. There exist good vegetarian and vegan diets with appropriate amounts of fat and appropriate total calories, and they don't at all resemble "brown rice, steamed chicken breast, and cauliflower".

Vegetables usually have carbs, and some have a lot of sugar. Whole grains are carbs.

If carbs are bad, you can't have those.

Carbs aren't "bad". You should be getting around 40% of your calories from carbs.

The problem is that some foods have nothing but carbs, and if you eat a lot of those, you'll either consume too many calories overall or fail to get necessary nutrients. So eat fewer white, starchy foods like potatoes, and more leafy foods, squashes, and other colorful foods.

Similarly, whole grains bring a lot of vitamins and fiber, while refined grains like white rice are reduced to just the starch. It's just fine that those whole grains also have carbs in them. That's actually a good thing, becuase you do need calories for energy. You just need more than that.

Lack of exercise is Most Bad. If healthy living were a decision tree, amount of exercise each day would absolutely be the root node.

Most people can get away with eating whatever they want with a modest amount of rigorous exercise each day. Granted, they still need to control their food intake and ensure they are getting required nutrients, but that's pretty straightforward.