Sine Wave "Lobes" (Basics, and probably a dumb question)
You're just seeing the amplitude of the individual samples, not the wave that travels between them.    If you generate a high-frequency sine wave, you will see that the samples don't necessarily go anywhere close to the actual peaks of the wave.
At some points, it looks like you might expect, with samples near the peaks of the waveform:

but at others, the samples are not near the actual peak of the waveform:

(These are both from a 12.001 kHz wave viewed in Ocenaudio sampled at 48 kHz)
If you are displaying only the samples (as you are in matplotlib because it does only linear interpolation between them), then you will see this as &quot;lobes&quot; that go up and down as the samples move closer and farther from the actual peaks.  But the actual waveform the samples represent does not go up and down, it's constant.