My thoughts are that providing a context for learning the science is too important to skip and it should be woven into the entire chapter/section rather than held in its own separate section isolated from the other content. From my own experience with text books, I believe science teachers skip the context at the beginning because it is not relevant to their students.
So here is where the online text book comes in. Teachers are free to edit, modify, take out sections, add sections and do whatever to the text chapter of the online text book. They can add information to the bone dry second part from the first part to weave the two together and contextualize the information. They can add or subtract information or change the wording to make the text more culturally relevant. This means each year you can change it up based on the passions and identities of your particular students. Online open source textbooks are tools for equity in education.