Some I think are down to genetics and health conditions. Not ALL but some.
Up until I was 19, I was stick thin - when at school in my teens, teachers questioned my parents as to whether I had an eating disorder because I was so thin. I didn't! I willingly went home every day eager for dinner.
Anyway, after 19, bit by bit I started gaining weight. At the time I hadn't long left college and put it down to not getting quite as much exercise as usual. So, along with my mum I joined a gym and went 5 days a week - the gym followed by a swimming session. Still, quite rapidly the weight piled on, along with other symtpoms such as excess hair growing in places it shouldn't. Upon going to the doctors when I failed to control it, they found I had too much testosterone in my body which was the cause. It took them a further 2 yrs to find out why this was happening. Turned out I had polycystic ovaries.
Now, whilst it's certainly not impossible to lose weight with such a condition - it's bloody difficult to say the least!
I didn't drive until last year. For 3 years I worked a full time job, on my feet ALL day and walked 3 miles each way to and from work. I started at 4:30am so no buses available to get there at that time. I've never been one for breakfast (could well be a contributing factor) so never ate anything until around 12 - which was more often than not a sandwich with fruit. During the times I was actively dieting, I'd then go home (3 mile walk) at around 4:30pm and have a meal of chicken and salad, or a roast without the trimmings...maybe a weight watchers meal - something along those lines.
After all this, I also had a dog who needed a walk each night so there was another trapse around fields etc for an hour.
Did I lose weight with all that? Not at all! I never gained but never lost either. To eat any less than what I was already doing would have been absurd (in my opinion - some may argue).
I then had an office job for another 2 1/2 yrs after this (before having DS). It was much further away, involved long periods of sitting down and for most of the journey I caught a bus - although from home to the bus stop was nearly a mile the drive way where I worked alone was just over a mile long (situated in woods). I left the house each day at 7:30am and returned at the same time in the evening to, again walk a dog. When I arrived at work in the mornings, I tried to get into the habit of eating something, so would usually have a slice of toast, some fruit or a small bowl of cereal. My lunch often consisted of much the same thing - weetabix or fruit. Then I'd have any sort of meal at home - fish, potatoes, veg sort of meals. Colleagues of mine, who were much thinner ate a lot more than I did during a working day. I remember watching my boss have breakfast at 9, followed by a sandwich, crisps etc at 11 then a normal lunch between 1 and 2. And then talk about "whats for tea". And she was stick thin. Chocolates, cake, biscuits etc were consumed regularly and I couldn't help but feel the unfairness of it all.
Now DS has come along, although I am obviously quite busy with him and on the move in the day, I don't actively exercise and my eating habbits are more hit and miss. I can munch on a couple of biscuits when it's more convenient, drink quite a bit of coffee, more likely to eat a sandwich (or 2!) for dinner rather than cook something - after cooking for DS I often cba. In the evenings I'm so tired I just crash and sit on my arse for most of it until bed time, sometimes with a packet of crisps or even a chocolate bar. I could definitely understand my habits now causing weight gain. But, funnily enough, 2 yrs on and I've actually lost a bit (noticable to others) for the first time in bloody years - and without trying!
I do hope it continues. But, to blame EVERY fat case on eating shite and never exercising, I think is extreme because it definitely is not ALWAYS the case. Should I continue losing weight (I'm certainly hoping), perhaps one day I'll become 'normal' again and people will then make assumptions that I don't eat junk and regularly exercise - and how wrong they'd now be!