It’s all driven by the math used in the NP formula. In the following examples, let’s assume the NP formula uses a 2 second rolling average instead of 30 second, and the workouts are very short 
(the concept is the same when you extend to 30 second rolling average and longer workouts, just makes it easier to see in an example).
Workout #1 (second: FTP%):
1: 0%
2: 100%
3: 0%
4: 100%
5: 0%
NP = ((0.5^4 * 4)/4)^1/4 = 0.5 = 50%
Average power = 40%
Workout #2 (second: FTP%):
1: 0%
2: 100%
3: 100%
4: 0%
5: 0%
NP = ((0.5^4 + 1^4 + 0.5^4)/4)^1/4 = 0.73 = 73%
Average power = 40%
So both workouts have the same average power, but workout #2 has higher NP due to the 2 second block at 100% FTP.
Intuitively this makes sense - it’s harder to do a single block at 2x duration vs 2 blocks at 1x duration with a rest interval in between.