Why was culture change a slow process in earlier times?

One of the main ways how cultures change is through contact with other cultures.

In earlier days, people could not be informed about other cultures as quickly as they are now (through TV, Internet and other media). Often, they had to wait for people to come back from journeys that took years, and then they didn't have a direct contact with the other cultures as we have today (for example sushi places all around the world)