I'm going to make a guess based on my limited experience here. Any Portuguese players feel free to correct me.
Portugal is far away from central Europe and traveling is already expensive because the Portuguese economic scale is a lot different. Income is lower, but so is the cost of living. On average, life here is very much the same as in other places in Europe, but intra-continental traveling is a lot more expensive because naturally the cost of travel is not adjusted for lower Portuguese incomes.
I.e. a 150 euro train ticket to Holland is about 30% of average monthly income here.
I believe they have gone to Spanish internationals, though.