What is often not acknowledged or even mentioned is that many people have difficulty with fasting because they are addicted to food - either addicted because of euphoric and opiate numbing effects that wheat specifically can cause, or from the numbing of sugar and carbohydrates - as inflammation has a depressant effect on the nervous system. The addiction to food is also self-medicating. If people don't realize this then they will struggle more than they need to. Reducing food intake if you're dependant on that breakfast with wheat and sugar-carbs to numb your nervous system, to calm your current emotions and perhaps pressure from past unhealed/unprocessed trauma, then as you reduce your food intake you're going to get exposed to withdrawals, as well as start being able to feel what's underlying - and you may not understand it nor know how to process it; this is certainly why intermittent fasting is perhaps healthier, gentler, and more sustainable for people to succeed at - as it won't apply or re-expose them to as much pressure with the quelling-numbing effects of many if not most foods.

Another part to why fasting can be difficult for people is as your inflammation level goes down, so does the depressant-numbing effect, so you will feel whatever digestive pains and irritation some of the foods you're eating may be causing you more clearly; this coincides with most people commenting how their thinking and senses become much sharper as they deepen into the length of a fast. If you're regularly eating foods you don't realize are agitating your GI tract, any that are causing inflammation, then the potential for fasting to be an enjoyable and easy endeavour for upkeep - weight loss or maintenance - will go down.

Edit to add: There may also be mild to severe dis-ease progression, damage/injury to the GI tract from lifelong lack of awareness (being numbed from eating foods that are harmful to you by some of the foods you may/likely have been eating) allowing the damage to progress. You may then be exposed and feeling this pain and then eating again is how you numb feeling it as strongly. Likewise there are bacterial infections that will benefit from fasting, cutting off their food supply greatly - much like why fasting can be beneficial for cancer growth - however, h.pylori bacterial infection for example causes nausea only on an empty stomach - and so that could be why some people are constantly driven to eat, not only to numb themselves but also to reduce nausea without realizing what's actually going on. That's why I also recommend microbiome stool testing. Also, if you underlying physical pain and injuries, reducing the inflammation from food will also increase your perception (and reaction to) to that physical pain - and so until you get that underlying pain treated then you'll be in a more agitated, less numbed state as well.

All of what I said above is ultimately why a practice of non-violence is necessary, non-violence towards others but also non-violence towards yourself: be gentle on yourself. I feel it's also important to state that all of this learning is a practice, an experiment you run through with yourself to understand yourself more and how things like food affect you, how breath affects you, how the mind affects you.