Why did the dark grey color of bricks change?
(I can't believe this hasn't been asked yet, so I'm still looking for a duplicate.)

In a nutshell, yes, everybody noticed and it was actually one of the biggest consumer backlash  the LEGO company had to endure. Fans vowed to never play with LEGO again, and so on. The fact that the LEGO company did the change unannounced, and even happily mixed both palettes in some sets, didn't help. Then they said the new colours were there to stay, and nowadays I'm not sure there are many fans left holding a grudge against this (apart from the ones who did really quit the hobby, I suppose, but then they aren't fans anymore, are they?)

And no, it wasn't a matter of factory change but a deliberate change to make the overall palette more satisfying and attractive for children, who are the target consumers of the LEGO company. Case in point, kids nowadays don't know about the old grays, and don't usually care.