The underlying circumstances* in the two cases were the same. YOU chose to ignore that and focused on the type of commerce being regulated. Since the type of commerce was different, you opened your yap and embarrassed yourself.
* From The Shreveport Rate Cases, 1914:
"It is for Congress to supply the needed correction where the relation between intrastate and interstate rates presents the evil to be corrected, and this it may do completely, by reason of its control over the interstate carrier in all matters having such a close and substantial relation to interstate commerce that it is necessary or appropriate to exercise the control for the effective government of that commerce."
Controlling an intrastate activity that is related to interstate commerce is the underlying circumstance.
I'm not embarrassed at all. They weren't regulating intrastate commerce, they were regulating the actions of the carriers, and any involvement of intrastate commerce was incicental and irrelevant to the outcome.
"It is for Congress to supply the needed correction where the relation between intrastate and interstate rates presents the evil to be corrected, and this it may do completely, by reason of its control over the interstate carrier in all matters having such a close and substantial relation to interstate commerce that it is necessary or appropriate to exercise the control for the effective government of that commerce."
What was relevant was that they were interstate carriers. Once that was established, the intrastate commerce issue was irrelevant. No carrier, no reason of control.