> I heard there used to be dozens of plane-building companies when the field was unregulated, with new, more efficient models and lower prices appearing regularly. I wonder what happened.

I heard that this is nonsense. There never were more than a handful of large aircraft builders (still are plenty of small ones), safety records certainly weren't better in the era before consolidation, and new entrants funded by the might of their governments have failed not because of regulation but because what airlines actually want is lots of identical aircraft from a reliable supplier and the new entrants haven't really been competitive in terms of performance either. The certification is complex, but so's building an aircraft, and it's really only the people further down the supply chain that need the protective umbrella...