Interaction between FigureWidget constructor and Javascript?

I’ve been looking into trying to better understand the connection between plotly.py classes and the frontend. Looking within the source_code, I see the existence of various message methods like: _send_addTraces_message and send_moveTraces_msg.

When I step through the code or add traces to an existing FigureWidget object, messages fire as I expect. However, when I create a Figure object, and then pass that into a FigureWidget constructor I don’t see any messages fire, even though the figure is created. Ex below:

import plotly.graph_objects as go

fig = go.Figure(x=[1, 2, 3], y=[4, 5, 6])
fig_wid = go.FigureWidget(fig)   # Don't seem to see any of the messages firing 

So my question is: what (alternative) process is taking place in the situation above?