It's less the airlines being cautious
(like they finally started being
over Ukraine, but not until MH17)
You are misrecalling the chronology. Some airlines such as British Airways were avoiding that airspace before MH17 was shot down, it was making the news beforehand. Other airlines such as Malaysia Airlines continued rolling the dice on flying in an active warzone.
What changed after MH17 was that avoiding it was mandated by the relevant authorities.
What changed after MH17 was that avoiding it was mandated by the relevant authorities.