I wonder what this is referring to. All the Yahoo products I'm familiar with (admittedly not many of them), could be adapted to mobile. Yahoo Answers could have become completely addictive if easily accessible. Looking at a list of all their other services on Wiki, I can't find a single one that "[wouldn't] work on mobile".
The phrase "didn't work" is a cop out. If something "won't work" or "isn't possible", then you just haven't thought of a good way to make it. Don't pretend like things can't adapt and change.