To be fair, the exodus was more to do with them promoting paid content and less to do with the UI changes.

I never really used Digg myself, so I can't speak from personal experience, but I wonder how much is due to utility. A lot of the new user interfaces I see these days simply do not have the same utility as older ones did; there's been a clear trend in dumbing things down, called "minimalism". Just look at Gnome3; they removed all kinds of configuration options.

Reddit is a very "busy" site. But you can do a LOT on it; there's many different features packed into it. The same thing happened over on Slashdot: the old versions had more features, and their "Beta" version tried to "simplify" things which really meant removing features.