>I think you may be confusing "agenda" with "perspective". He was pushing one perspective: his own, as all authors do.
If you're used to science, it can come as a surprise that a person can willfully ignore (not just focus away from, ignore), all but one option for an entire book, and it still be considered an intellectual effort as opposed to a sales pitch or campaign tool.
To be honest most of the times he lists the multiple concurrent theories and simply points out why he believes one of them to be closest to reality.
Of course, sometimes none of the theories can be proven or disproved. So unless you want to leave a black hole you simply choose the theory that fits best, with the risk of it being overturned in the future.
If you're used to science, it can come as a surprise that a person can willfully ignore (not just focus away from, ignore), all but one option for an entire book, and it still be considered an intellectual effort as opposed to a sales pitch or campaign tool.