Because during the Napoleonic wars Spain was in upheaveal and the colonies were left to themselves and so of course their would be panicked. But it doesn't change the facts on the ground that in the early 1800s the US had other worries than Louisiana. The natives under Tecumseh were organizing in the Northwest. The British and Americans were being drawn closer into conflict. The only reason France sold Louisiana was because it failed to put down the Haitian rebellion and lacked no foreword base from which to go into America.
Except the Spanish were also afraid, in the 1790s, of America seizing Florida and Louisiana, and officials in the region were very worried that nothing would stop the US. So were these guys crazy?