And why, pray tell, would you expect them to change? To what evolutionary advantage would such a change be put? Evolutionary change doesn’t simply happen in a vacuum, it happens in a real world where organisms compete with one another in an ecosystem and not all survive. What change would you expect in 6,000 generations of fruit flies born and living in a science lab?
They were exposed to different elements and conditions. I would expect them to still be fruit flies in 600,000 generations.