The police most definitely asked the husband why he didn't find it unusual that she was away for 5 days and her cell phone and car were at home, I doubt that his explanation was accepted at face value. Police would have asked if Shannon normally vanished without her phone and car for five days, and from what we heard at the press conference, the answer was no. There's nothing the husband could say that would make her disappearance sound normal ... meaning there's nothing he could say that would excuse the fact that he did not notify anyone about her disappearance, or that he waited until he got home from work to respond to her family's frantic calls.
I understand what you're saying, but if LE were convinced it was a criminal case, wouldn't they have launched a criminal investigation and gathered evidence from the home and the car? I don't think it's possible for them to do that secretly, they have to get a warrant.
What I'm saying is that LE doesn't investigate every disappearance as a crime, but they will investigate if the family is convinced it was a crime. In this case, the family seems to have been convinced it was a voluntary disappearance. I don't believe LE could tell family members to follow a script at a news conference and pretend to believe she's still out there, when they were deeply suspicious that she's not.
In the case of Tim Bosma, within a couple of hours of his leaving his wife reported it to police and it was immediately treated as a criminal case. They didn't hold a press conference where she told him he didn't have to come home but at least let me know you're alright. The family was convinced it must have been a kidnapping, and the investigation followed that scenario.
In another case, a Calgary man went missing, he was known to be a hiker, so they put out the word about his car and it was found at a Banff trailhead. Because his friends reported he might have gone base-jumping, police didn't investigate any further, by, for example, searching his car for signs of blood, inventorying his home to figure out what he was last seen wearing. He has never been found, but they aren't treating it as a criminal case because the family is convinced he died in an accident.
So what I'm saying is, while to me this case seems suspicious, there must have been some (or at least, was some) solid reason for the family to believe it was voluntary disappearance, and LE have followed their lead. I don't know what those reasons are, and the family isn't telling.