[bsder]

And most families only had a single car prior to 1980.

What's your point?

Did airlines get cheaper due to deregulation or because technology and engineering made operating them cheaper?

[SecretDreams]

Or as simple as incomes crept up and airlines reduced some amenities - both allowing for increased ridership which helped to reduce per head costs.

[tt24]

Probably mostly deregulation and a little bit the latter