The Line Similarity tool will not show any information in a Line Chart whose lines all have different start points and/or end points on the X-axis. This is as designed. It is a known limitation of the algorithm used in the Line Similarity tool.

Fig 1. (See the attached "KB-44470.pdf" file.)

In Fig 1, the Line Similarity tool does not produce any information. The first start point of any line is 5/18/2010, and the last end point is 12/30/2012. Unfortunately, not even one line covers that complete length of time.  The "Compact" vehicle type comes close, but its end point is only 11/14/2012.

Fig 2. (See the attached "KB-44470.pdf" file.)

In Fig 2, The X-axis has been filtered down to between 2/28/2010 and 6/12/2012. Here the line for the "Truck" vehicle type does cover the full X-axis range. Therefore, the line similarity is calculated for only this one line.  The other two lines are not as long so they do not cover the full range.
 
Fig 3. (See the attached "KB-44470.pdf" file.)

In Fig 3, the filter on the X-axis has been further limited, to 2/29/2012 and 5/22/2012. Here we have two lines showing. Both lines have exactly the same start point, 3/1/2012, and the same end point, 5/18/2012. Note that the lines' start points match and their end points also match, so Line Similarity is calculated for both lines.

This is as designed. It is a known limitation of the algorithm used in the Line Similarity tool, which requires identical endpoints.

Build the Line Chart using data whose X-axis start points all match and whose X-axis end points all match, for all lines--or filter the data on the Line Chart to achieve the same result.