See what I mean? You think that's the only way Congress can regulate.
"What was relevant was that they were interstate carriers."
I thought you were against expanding the Commerce Clause and here you end up defending that expansion. Carriers are not commerce. The Commerce Clause says "to regulate commerce", yet you defend the regulation of carriers. My, my, my. Be still my heart.
But, for once you're right. The courts have ruled that Congress may regulate the interstate carriers because, duh, interstate carriers have a substantial effect on interstate commerce. Shreveport came along and said that Congress may also regulate the carrier's intrastate activities -- not because they're carriers -- but because the carrier's intrastate activities have "such a close and substantial relation to interstate commerce".
The Shreveport court tied everything to interstate commerce, not the fact that they were carriers. Otherwise the court would have simply ruled that, since Congress has chosen to regulate the carriers, they may regulate all operations of the carriers irregardless of the effect on commerce. They didn't.
..by reason of its control over the interstate carrier...
It says what it says, and you're asserting otherwise, not matter how often or virulently will not change it.
If the court tied everything to interstate commerce regardless of who's doing it, then there would have been no need to establish the railroad as an interstate carrier, yet the bulk of their decision is dedicated to precisely that. Do you think they went through all of that only to get down to the end and say, "But none of that matters anyway, all that really matters is that they're affecting interstate commerce."?