The people of this country are divided, and the states can represent them far better. Public transportation, schools, fire departments, libraries — these things that benefit us are all local entities. Give the federal government a dollar and they’ll spend half of it blowing stuff up. States can form cooperatives (as they have with climate change) and come and leave various cooperatives without the complexity of the EU.
Half the country no longer believes the federal government can deliver public goods reliably and cost-effectively…and have plenty examples to prove it. Maybe that is the experiment that failed.