Because the values at other locations are not maximum: 162 instead of 163.
>> L([31 57 83 109 135])
ans =
163 162 162 162 162
If you want to find some extreme pickes you can try;
>> pick_location = find(L>160)
pick_location =
31 57 83 109 135 136
To actually find peaks try PEAKFINDER submission from FileExchange.
4
solved Matlab, get the peaks in a vector, this does not work: max_locations = find(A==max(A)) [duplicate]