I work that out by observation & thinking. It's not difficult.
Cheap airline tickets emerged from a change of airline policies about pricing. I remember the time before cheap air travel.
Various low cost airlines (for example, RyanAir) introduced a demand-based 'dynamic pricing' model, at the same time as they stripped out and priced everything - bar the actual flight - as paid-for extras.
And then used that model to drop the base price of the flight.
This was mostly for short haul travel. It's interesting that there are far fewer airlines which use this model for long haul travel (anything over 8 hours). Apart from the appalling Scoot Airlines (cheap offshoot of Singapore Airlines - avoid, avoid, avoid.
It might be (I don't run an airline) that passengers are far less prepared to put up with RyanAir style conditions on a trip to Australia or the US west coast.
The cheap airline/base price/short haul argument runs that you pay a base price for a flight to get you from A to B, and that price is dynamically priced (higher at popular times, lower at less popular times). You then add the things that are important to you - seat choice, hold luggage, big cabin bag etc etc.
It means that if Person A is happy to sit anywhere and carry very little, they pay for that. If Person B prefers a particular seat & wants to bring a cabin bag on the flight, she pays for that. And so on.
It's not rocket science to work out that if international law & industry standards required that families are seated together as a priority and without extra 'seat choice' payment, airlines using this base-price model will attempt to recoup income elsewhere.
The opinion that airlines should not price this way is a whole other argument.