They were kind of the definitive site for general information in the 90s, so many millions of people who started using the internet in the 90s got used to going there for news, sports, finance, weather, and some of their other verticals, as well as things like email.

A lot of those people haven't had any good reason to switch to anything else, so that's what they use. This tracks with the way people choose offline brands like toothpaste and such -- once people get used to buying a brand, most of them tend to stick with it until they have a clear reason to change.

That's actually why the transition to mobile is so crucial for them -- those people still want to keep up with sports and weather and everything else on their phones, but they're more likely to use an app than a website. If Yahoo loses their userbase in the transition to mobile, those users are probably never coming back.