It changes the way we think about the world and about ourselves, sometimes for hundreds or thousands of years. Good theory is embedded in our lives with such familiarity and naturality, that we no longer recognize it as theory. This means that both fashion designers and IS authors apply theories. They just don't realize it. Theoretically speaking, the IS field has no time to pay attention to what it is doing.
Nobody has time to think.
Moreover, thinking is not appreciated. It doesn't sell. Theory does not sell. It takes too much time. As a result of 'effectiveness' and 'efficiency' mania, among other things, we have created the 'publish or perish' mentality of the American academia.