Probably concern about zoonotic diseases and invasive species. Florida citrus farmers are suffering from imported plant diseases and insects, released pets that have become invasive and that devour native wildlife and so on. Not unlike concern about transporting unvetted/illegals all over the country risking disease and crime.
Invasive species are largely the fault of government releasing invasives to mitigate problems caused by invasives. These are problems caused by the very government that now seeks to destroy vast industry as penance for their arrogance.
It is especially disturbing that such a draconian fix could be proposed by a Senator who represents the very interests he seeks to destroy.
The pet industry is not at fault for destructive invasive species. Government had its hand in every instance of serious destructive invasive species. Of the 20K species of animal imported into the US less than a dozen have created any serious problem. This is akin to shutting down the entire auto industry to stop auto accidents.