-It's a common market, so not import taxes are allowed. That means that any new industry will have to compete with developed companies already established.
-Public companies are encourage to be privatized, so, you can't keep an industrial base that it's not, for now, competitive.
-The result is desindustrialization. Then those desindustrialized countries are accused of not being competitive.
-In some cases, at the European level they realize that they are losing the strategic edge to other blocks, and some kind of program at the federal level is created. Like the current thing with the chips. Of course this programs never will result of giving the edge to one of the PIGS.
In practice this is gamed in many ways, and there have been winners and losers.