I don't think that's completely true. There is a combination of market size and regulatory burden; not a lot of people are buying GA aircraft (compared to say, the number of people buying iPhones), so there isn't an enormous financial incentive to get people out of their C172 or Bonanza.
I also think that these old airplanes are really ships of theseus. Maybe there are some original stickers and seats, but that's about it. Safety and avionics upgrades on these old airframes are definitely in the financial reach of many readers of this forum, and I'm sure many people are flying "old" airplanes that have AoA sensors and IFR-certified glass panels and backups. Day to day they probably feel a lot like airline pilots.
> many people are flying "old" airplanes that have AoA sensors and IFR-certified glass panels and backups
Yes and no. They're out there, but they aren't as common as you'd think or hope. AoA in particular is rare. There's an awful lot of planes that are still running GNS430 or GNS530s (probably more than any other single setup), and more than a few with the original nav/comm equipment like the KX170B. A real glass panel (something like the G1000 or G3X) is really rare in an old plane. Maybe 5-10%?
I also think that these old airplanes are really ships of theseus. Maybe there are some original stickers and seats, but that's about it. Safety and avionics upgrades on these old airframes are definitely in the financial reach of many readers of this forum, and I'm sure many people are flying "old" airplanes that have AoA sensors and IFR-certified glass panels and backups. Day to day they probably feel a lot like airline pilots.