I do not get the impression that this puts pressure on the weaker governments to reform.
People decide to move when the advantages of moving outweigh the relocation costs. Sweden might be a better run country than Greece, but personal relocation costs are high (mainly due to the language barrier). In the US, the relocation costs are much smaller but moving from one state to another makes little practical difference for most people (compared to the central government the states have little actual power).
State and local governments in the US have primary responsibility over education, road construction, utilities, policing, the courts, licensing restrictions, zoning laws, and public transportation. The federal government can and does sometimes overrule them in these areas, but they are mostly left to themselves. Federal government action tends to be restricted towards various welfare programs, foreign policy, and the health care system. I would not describe state and local governments as having little power.

Historically, the evolution of government systems was mainly driven by violence, with invasions and revolutions being the principal agents of selection process. The rules of the game were predetermined by our environment - land was a limited resource, for which our ancestors had to compete, if only to ensure the survival of their descendants.
The 20th century introduced a game changer. As agricultural productivity in developed countries rose by orders of magnitude and natural population growth practically came to a halt, possessing a large territory stopped being a necessity. Countries with little arable land, ultra-high population density and no natural resources can now not only feed their population, but also achieve top living standards. These changes may open a fundamentally different route for societal evolution – one that would not be based on violence or compulsion.
A small thought experiment - imagine what would happen if central governments cede most powers to smaller territorial units:
Unfortunately, there are serious obstacles to the successful implementation of this idea:
Do you think these problems are solvable?