The huge changes to the Yahoo mail service were put in place by their new CEO, who, like all new brooms, just has to sweep everything clean.
The Yahoo using public HATES the new changes. Find any discussion thread about it, and you'll have a hard time finding a single complimentary comment. The public has been screaming at the top of their lungs about it for months now, and Yahoo hasn't done a thing to abide by their customers' wishes.
Reminds me of the "New Coke."