Part of the problem with the
Mini 3 is that it can be under or over 250 g, depending on the battery (not counting any extra accessories). If 250 g is a legal bright line that can be crossed simply by changing the battery, I can see the manufacturer opting for the (legally) safe approach of assuming use of a plus battery in complying with any regulations.
(Assuming the drone knows which battery it has installed, code could easily adjust its behaviour accordingly, but at the risk of a bug leading to non-compliance. Safer to have a behaviour 'always on'.)