I didn't see the reason clearly spelled out, but I found this comment from a guy involved in the search interesting:

A setback like this would have required waiting for a day for the creeks to subside (best case scenario). This would have put them without food for a day, and a day late at the trailhead (again, best case), which would have probably called SAR anyway. Of course, being in the bush they had no idea what the weather forecast was!

While he did imply that they weren't prepared enough, he also suggested that even if they were prepared to wait things out, a search would likely have been started due to their not getting out on schedule (he also suggested their planned time-lines were too tight).

I think this is one area where a SPOT can be considered an asset, as demonstrated by an earlier commenter on that same thread:

I almost always have one of my buttons programmed to say "I am ok but will be late" so that no one calls out an unneeded search if I am just delayed.