No, this is not the reason. If the camera records video for more than 30min, then it is a video camera, see the question answered here https://news.ycombinator.com/item?id=34640107
In short, there is no good reason anymore, but originally this was because of EU import tarifs.
It's not a joke, older DSLR cameras would often overheat when recording continuously. My good old Canon 6D would overheat once in a while when used as a webcam with v4l2loopback.
Even as recently as the Canon R5 Mark I mirrorless camera (which you can still buy new), overheats within 15 minutes if you're recording 8K30 or 4K120.
IT's not a joke. When filming for more than 30 minutes the cameras at the time (10-15 years ago) would warm up and eventually shut off automatically to cool off.
In short, there is no good reason anymore, but originally this was because of EU import tarifs.