There are a lot of things which work better as federal programs vs state / local programs. Homeless populations spring to mind, if some city's treat there homeless population poorly they can 'export' the problem to another city / state. Where a state with overly generous benefits may see migration.
Education is another with states that export there most educated population having little incentive to subsidize their higher education system. Which likely has lead to the dismantling of state funded schools as people became more mobile.
> Which likely has lead to the dismantling of state funded schools
I disagree this is a necessary outcome. It may as well happen that backward states will take notice and improve their higher education system in various ways.
But I think what you are saying is a fair point and I actually mentioned it. What I would add to my comment is the common solution to this is called "principle of subsidiarity" and it's used EU and Switzerland (which is another example of a federation that often tests different law variations in smaller scale first).
Education is another with states that export there most educated population having little incentive to subsidize their higher education system. Which likely has lead to the dismantling of state funded schools as people became more mobile.