Many people will do things like use Google Travel to narrow down an initial set of potential flights based on times & cost, and then go to the individual airlines from there to book things. The GPs post is still a problem in this scenario.

That seems like a Google problem because of a poor interface. Unless you want each airline to standardize their offerings. Even then their would be differences based on loyalty programs, which airline you have a credit card for etc.

The legislation nor the regulations were geared toward third party aggregators.

Kayak has a flag to limit tickets shown to only those sold by airlines. That's the way to go.

Google Flights isn’t a third party portal! It takes you directly to the airline web site to book. It attempts to estimate the fare price but that’s becoming increasingly difficult with variably priced seats and other “gotcha” expenses that get figured in deep into the booking flow.

For domestic flights, perhaps. It routinely refers me to third party OTAs for the cheapest prices on flights to less common international destinations.

And in that case, this was never regulated by the government. The airlines shouldn’t be responsible for how their products are presented on a random aggregator.