I think you are hugely underestimating the influence this book had. This was the first catalog including these patterns and the authors gathered them by looking at source code from many, many projects and compiled common patterns they deemed useful into this book. They named the patterns and this book ultimately popularised them. The book was a huge success when it first came out and I know many people who have indeed read the book. I've even encountered it in university twice. Without this book many of these patterns might not have a name and hardly anybody would know them. They would be patterns in the way that they randomly occur in the wild, but not in the sense that they are templates that developers seek out to solve problems.