It actually has a lot to do with history.

The most important thing to understand, I think, is the way the Industrial Revolution spread through Europe. As you may have learned, England was the starting point. What made England special? Firstly, goods and people could be moved fairly cheaply compared to the continent: there were no internal tariffs, you could ship goods up and down the coast line since England was an island. Secondly, there were plenty of natural resources, both within the UK and in the colonies. Thirdly, the rise of enclosure left a lot of peasants without land: this meant that there was a force of unemployed workers that could be exploited. This is why wages were tied to the price of bread: the idea was that if a family had to work to have enough to eat each day, there would be more motivation to work. Couple that with the fact that England has had more or less the same political regime since the Industrial Revolution (a parliamentary monarchy).

France and Germany had a harder time of it, but still had the advantage of colonies and raw materials. They also played off each other in various wars, which gave them motivations to industrialize. France had unified after the French Revolution and Germany had unified under Bismarck.

However, the South of Europe (Portugal, Italy, Greece and Spain) were never fully industrialized. Even today, Italy, Greece, Spain and Portugal are primarily agricultural countries. They also did not long benefit from colonies: Italy managed to take Ethiopia in Africa, but did not hold it for long; Spain, on the other hand, decided to take on the US and lost its last important colonies. Portugal held on far longer, but did not exercise much control over its colonies and had lost its most important colony, Brazil, soon after the Industrial Revolution had begun in Northern Europe. The Greeks managed to succeed from the Ottoman Empire, but they were comparatively a very young nation that got involved in the Balkans wars with Croatia, Bosnia, Albania, Macedonia, Serbia, Bulgaria, Romanians, Turks, Slovenes, and Montenegrins. They were pretty much crushed. Then they were invaded by fascist Italy during WWII; even though they managed to fend off the Italians, Nazi Germany came in to bail their ally out and both the Allies and the Axis bombed Greece at some point.

The other problem is that these countries do not have very many resources for industrialization. Portugal in particular is dependent on other countries for wheat. Portugal, Spain, and Italy have all had totalitarian, fascist dictators (Salazar, Franco, and Mussolini). Italy's fascist regime ended after WWII, but Salazar's and Franco's regimes continued into the mid to late 20th century. Italy has also been plagued by corruption since WWII.

All this means that Portugal, Italy, Spain, and Greece were not really able to industrialize until much later than the UK, France and Germany. When the European Union was formed, these countries took advantage of other EU members' money to try and modernize their economy. The problem is that after several years, the recession came along and they're not returning well on their investments. This means that they default on these old loans, they take austerity measures, and austerity measures in turn make people unhappy; hence, they are less likely to consume certain products, which makes the economy even worse.