In advertising, why is imagery more important than just words?

I wouldn't say it is more important than just words. In advertising, it is all about impact. The value of a great image is only in how well it captures the viewers attention. If a provocative image can do that, then so be it. Similarly, I've created ads that are little more than words, but their effectiveness lies in the ability to hit directly on a pain point. Good ads can capture attention through humor, provocation and good old fear, uncertainty and doubt.