That's not the right framework. It's better to see it as the logistics of parcels: the carrier doesn't create customs regulations or import taxes, it applies them and informs you of what's necessary for your parcel to arrive.
Flight platforms only present travel requirements; they don't set them.
The validity of your passport or the need for a visa are sovereign decisions of countries, not search algorithms.
For example, even if Google Flights shows you a direct flight to a country, it doesn't mean you can enter without a visa if your nationality requires one.