They must have some use case in mind for the 16GB options, unlike previously where extra RAM has been for a specific feature, or ‘to manage extra storage’* it’s a bit ridiculous to include an extra 8GB for this rather than say an extra 2GB. My expectation is it will only be relevant for a few specific pro apps, like final cut, as well as helping with system function etc. At most it will be like procreate where more ram allows for more layers, to avoid Android style fragmentation.
* if I remember developers had to treat the 1TB 2018 iPad Pro’s the same as the other configurations though so the extra RAM isn’t a factor (at least for 3rd party apps) there, or was this retconned when the 2020 arrived?