Oh I know, lets introduce a field that stores an array of your nationalities, so any app developer can request your nationalities and adequately fine you for spreading illegal content online if you are Russian citizen.
In this hypothetical situation, why are you choosing to install software that does this? This software could just as easily store the data in a flat text file in your .config directory, it doesn't need systemd in order to exist. Systemd choosing to not add those fields would not prevent the software from existing.
In any hypothetical situation where you're forced to use some hypothetical privacy invading software, that software would still be able to do everything exactly the same even if it has to store your information outside of systemd.
Not having a field in systemd doesn't mean that the data can't be stored, it just means that the data has to be stored in a text file instead.
Systemd also has fields to store your realName and location. That same hypothetical situation applies to that data too. Your REAL NAME gives much more information about you than your birthDate and the location field is big enough to store your exact GPS coordinates. Like birthDate, these fields are not a problem (they've existed since the 60s) if you don't install software that uses them.
If you don't want software that tracks your location, don't install software that tracks your location. If you don't want software that requires your real name, then don't install software that requires your real name.
If you don't want software that requires your birthDate for age verification, then don't install software that requires your birthDate for age verification.