One reason may be that for your factor no DNA binding sites are available, yet, or that a weight matrix does not meet Genomatix' quality standards. Transcription factors usually bind in a defined orientation to the DNA double helix. This orientation depends on the orientation of the DNA sequence they recognize, i.e. their transcription factor binding site. An exception are factors that recognize symmetric or palindromic sites. In this case the factor can bind principally in both orientations.
Most transcription factor binding sites can occur in both orientations in promoters or enhancers.
In addition, there is a technical aspect that has to be considered. Each matrix has a strand orientation which depends on the strand orientation of its training sequences used. GEMS Launcher found a transcription factor binding site with a matrix similarity of 0.81. You have to compare the value of 0.81 to the optimized matrix similarity defined for the weigth matrix that represents the transcription factor binding site. On average, for most matches a matrix similarity of 0.85 will imply a good match.