I don't understand why Yahoo doesn't try charging for it. Monetizing it was tough, definitely, but it's been shown that actually CHARGING customers (as opposed to going with a straight advertising model can work).
If you're going to shut it down anyway, what's the harm in trying? Maybe have a "stay of execution" for a quarter - tell users you're going to charge $10/month for the service, and see how many users sign up. If you can break even, why not keep it?