The same way people underestimate their caloric intake, I think unfortunately a lot of fitness apps and equipment overestimate calories burned. A recent 1 hr peloton class I did said said I burned a little over 1,200 calories. It was nearly 300 more than my Whoop band said I lost. I think both numbers were higher than what I actually did.
In my anecdotal experience my fitness apps generally underestimates calories burned while exercise equipment generally overestimates it. Like how my Garmin watch told me yesterday that I burned 300 kcal from running 10 km which is nonsense. It should be around 600 kcal if you do a rough estimation.
The problem with calorie counting and fitness trackers is that they assume all bodies are equally efficient, a calorie is a calorie but a person is not a person. It’s like driving for 2 hours and trying to estimate how much gas to fill for the next 2 hours without overflowing the tank, all this based on the mpg of a standard car.