Yes it seems that now the police are working on the assumption that the abduction theory is the most likely, but how do you know this was the case at the start of their investigation? How do you not know that their investigations led them to this scenario as the most likely one? I'm not a police officer but surely when taking on a case like this, getting to the bottom of what happened would involve looking at the case from the beginning without preconceived ideas and looking at the most likely scenario (I've seen it in countless reconstructions and the book mind hunter talks about it as the most important aspect of detective work at any rate). To my inexperienced eye, that seems like the most obvious job of police work.
If right at the start they immediately focused on the abduction theory and dismissed everything else then that would be ridiculously incompetent and you would have to question why they are in the job they are in.