This is typically because they have timed out engines, are due for major inspections, or require expensive mandatory modifications such as RVSM or hushkits. That said, I know someone who purchased an original Lear 24 in the low 6 figures that needed everything. He spent more than 1M, but less than 2M on overhauled and hushkitted engines, overhauling and refinishing the airframe, major avionics update including ADS-B and RVSM, and other upgrades, and now had a machine that can FAR outperform an Eclipse 550 at lower cost. https://www.newunitedgoderich.com/projects/bombardier-learje...