Don't crimes usually have a motive?

I really don't see the point in something like this:

Police in central Minnesota said a man who claimed he was assaulted and robbed while helping two people was lying. Waite Park Police Chief Dave Bentrud said the 34-year-old Cold Spring man admitted to making the crime up, but it's unclear why.

The man had originally said he stopped Sept. 23 to help two men changing a flat tire at Stearns County roads 137 and 6, but instead the two men hit him in the head with a tire iron and robbed him.

The cops found that his injuries were self-inflicted, and now he may be facing charges for filing a false police report. Is it just me, or is this the worst crime ever?