In my experience (others will no doubt disagree) - Stress, sleep, UPF, hormonal changes, gut microbiome, genes, exercise, medication, insulin sensitivity - all play a part in appetite and how your body deals with calories from different foods.
Excess stress has an awful impact on our bodies and minds. The damage that stress can cause is massively under-rated by professionals.
Sleep deprivation; sleep is so important for a number of factors. It's been proven that a bad night sleep will cause you to eat more calories and usually 'bad' calories (i.e. UPF's).
UPF's have a lot to answer for. They are made purposefully to be over-eaten as they are manufactured to be addictive. It's been proven that UPF's can irrevocably change the neurotransmitter messages in the brain (see Chris van Tulleken's 'ultra processed people' book/TV program) so you eat the food item and your brain craves more so you eat more. It's designed to be eaten quickly so you eat more calories in the same time frame as you would eat a meal that you'd cooked from scratch.
Menopause wreaks havoc for some women. It's impossible to establish the exact science on how oestrogen, progesterone, testosterone fluctuations affect women's appetites and how the body deals with the food they eat because we are all individuals.
Gut microbiome - so much research is happening into this (the gut is the 2nd brain etc) and how bad microbes eat the good microbes in your gut if 'the wrong food for you' is eaten (i.e. some people have a low spike in blood sugars when they eat porridge whereas others have a massive spike) and this has an impact on your appetite.
From my own experience of weight gain/loss/maintenance over the years, all these factors play a part and that's before you've even eaten a calorie! There shouldn't be an 'eat less/move more' mantra anymore as Science is discovering that there are so many factors that contribute to someone's body shape, fat disposal/storage and appetites.
So, OP, I don't necessarily agree with your comment 100% "I don't believe any person is naturally obese without consuming a massive amount of calories either through food, drink or both" as obesity does occur in people because of factors out of their control. But of course there will always be some people that your comment would apply to.