Likely OP refers to individual countries and quarreling leaders often favoring national interests to what would be best for the union.

> leaders often favoring national interests to what would be best for the union

If we're talking about leaders for member states, then they're doing their job right :) They're not meant to figure out what's best for the union, we have separate elections for those people who go to EU and represent the country + care about the union. The national "leaders" of the country are quite expected to put national interests above what's best for the union :)