Today you can reach many times the people in a day or so that it would have taken weeks to contact by more traditional means. Your contacts benefit by filling out forms online and avoiding paper waste and postal costs. Let's face it. If you want to advertise, there are certainly many more proven methods than the internet. Newspapers know their exact circulation.
Television has ratings to determine viewership.
Direct mail is, well, direct. The internet is like all of these, and none of these. There are sites that are more like television where people may surf over to, spend a little time, then leave. By using a combination of proven and experimental methods. It takes time.