In a Line Chart whose lines all have different start and/or end points on the X-axis, the Line Similarity tool shows no information.

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

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

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

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.