Zillow will take your account info and send it to Realtors who bid for your phone number. Half the accounts they sell to Realtors aren't even interested in buying said home.
If that weren't bad enough they have so many outdated/nonexistent listings because the have no incentive to get rid of them. If a person clicks on it they get to sell your info to a realtor so why update it.
They are scamming both ends of the real estate market and not helping anyone find housing. Their estimates are also total crap because people are more likely to go through them if they give an unrealistic estimate