[V99]

It's really sort of the opposite. You don't see 727s or MD-80s at the terminal anymore (freight somewhat excepted). Airliners are used constantly, wear out and get replaced/sent to other countries. Buying another computer is a negligible cost in a new 787 or retrofit into anything an airline currently flies.

But there are tons of flying general aviation planes that are from the 50s/60's, and a long tail going back even further than that. Some of them don't even have a radio to talk on. Or an electrical system to run it.

Mandating ADSB took many years, and still has exceptions carved out. And that's a fairly simple technology. There are companies that build it all into a replacement tail light LED "bulb" to provide compliance for ~$2000.

Still that might be 5-10% of the value of your 1977 Cessna 152. If you take the cheap airframes out of the sky, that makes new pilots getting their 1500 hours more expensive before they can go get a job on the big boy planes.