@ptrblck  @tom   thank you very much for a quick and clear explanation.
When I use bias=False in the the preceding Linear layer, I see the indicator that all parameters have been updated.
I believe your response explains what I saw in a subsequent test I ran after posting my question.  In this later test, instead of doing only one backward pass with parameter updating, I ran multiple iterations.  In this test, I eventually saw the bias parameter updated after multiple iterations.  Sometimes it took up to 200 iterations for an update to be detected.
In other words, it took many iterations for the the effect of the very small bias gradients to “accumulate” enough to have an effect on parameter updating.
Again, thank you for your insights and the link to PyTorch performance guide.