E.g. for me, an hour of high intensity exercise five days a week still placed me firmly in the sedentary range.
Part of the issue is that we tend to "forget" about the hours spent at work when evaluating if we consider ourselves active.
As for intensity exercises, unless you actually measure your activity it will be difficult to estimate exactly how much time you're active inside of your hour exercise. I would guess a lot of people will over-estimate how much active time they really had. For example, weight lifting would be on the low side, HIIT classes somewhere in the middle and running/rowing/cycling on the high side.
Looking quickly at a few of them, they mostly have tdee estimates for my age now that were still to high for me at the peak of my exercise fitness a decade ago... That includes the calculators trying to take weight and height into account.
The issue is that most of these are repeating and deriving categories based on guidelines set at points in time when a much larger proportion of the population had jobs that involved physical exertion.
And so you can be much more active than average for todays population and still be considered sedentary relative to the activity levels assumed in guidelines.
E.g. the UK NHS guideline of 2500 kcal for an average male would take me adding a couple of hours of walking during the day to reach despite exercising more than average...
And I'm sure you're right that people's failure to estimate their activity when they are exercising or being active is also a big part of it.
Same goes when I go for hikes in summer. I am loosing weight, but I am walking at comfortable pace max.
I did not felt hungry at no point either. I dont know what it is, but intensity is not the only factor.