The EU says it must enlarge. But why did it stop in the first place?

Enlargement is regularly touted as the EU’s most effective foreign policy, but since its biggest wave of new members joined in 2004, the process has largely stalled.

The EU says it must enlarge. But why did it stop in the first place?
Enlargement is regularly touted as the EU’s most effective foreign policy, but since its biggest wave of new members joined in 2004, the process has largely stalled.