I think all trendy diets are essentially experiements that teach about viewing food in different ways. They're not necessarily meant to be done long term. Intermittent fasting teaches one that the body can survive without eating multiple times a day and helps one realize that sometimes they're not hungry, they're just bored or thirsty.

Eating vegan or vegetarian for health reasons teaches one that eating animal flesh or things that come from animals aren't necessary. It also helps one be creative in the kitchen when trying to make veg-friendly substitutes for foods like dairy-free icecream, tofu scramble, and chickpea or mushroom burgers.

Keto, paleo and other low-carb/starch diets, teaches one to not rely on carbohydrates that lack nutritional density and also helps one be creative in the kitchen when try to make substitutes for their favorites like cauliflower rice or baking with coconut flour.

I think people get caught up with the label of their diet/way of eating and forget to listen to their body. We shouldn't feel shamed for "breaking the rules." The purpose of eating is to properly fuel the body, not follow a list of rules. For some people, these trendy diets can be done long term. For others, it doesn't make sense to follow it 100%; they would be better off following it in doses.