commerce clause
something somewhere , some how , may be sold ... or may not be sold ...
If they can say growing grain to feed your own stock is regulatable via the commerce clause because you would have had to go out in to the open market and make a purchase ... but you didn’t because you grew your own , therefor impacting the world market prices of grain ...
then they can say anything is covered under the commerce clause.
it’s a another power grab
The Supreme Court just repeated that analysis a year or two ago in upholding federal laws against California's attempt to legalize growing your own marijuana for medical use. Even Scalia held that that was a valid use of the commerce clause, on the theory that if people can grow their own marijuana some of it might be diverted to interstate sales.
But in this case, however misguided the legislation is, I think it is constitutional under the copyrights clause combined with the necessary and proper clause; the commerce clause doesn't even have to enter into the analysis.