I agree but I see two reasons for the soulless, muted UI:
1. 25 years ago, computers and the internet was something new you wanted to attract people to, shiny new toys.
Today it is something people are gonna stare at 10 hours a day or more. I guess Windows XP was really tiring for the eyes after a while.
2. I believe the evolution we see in UI is exactly the same we saw in buildings and homes. I personally can't believe how depressing most modern houses are inside and outside.