When we dream about travelling, we do so because we think we'd be happier somewhere else. In fact, usually, the place doesn't matter, as long as it's just not here.
When we arrive and actually experience the destination, our old modes of thinking persist. We get bored, distracted, worry about details, and spend very little time taking it in.
Only in our memories of our journey does the trip take on an ephemeral form again, where we edit out and forget everything except the most potent few moments.