I have mixed feelings about this - having owned and repaired a lot of vehicles for my own use I don't think it's always true an engine will last half a million miles, just go watch the "I do cars" channel on youtube and you'll get some idea.

The big problem here is survivorship bias - the cars that did last will likely keep lasting. You see this with notoriously terrible cars like 1980s Jaguars. The owners have persisted through various catastrophic failures that would make ordinary people abandon the vehicle, so you end up with a subset of Jags that run nicely and have all the engineering problems sorted out by the after market.