I read an article the other day which suggested that due to the current value of the Euro against the Pound, it having an influence on players deciding to come to England to play football, and also something reguarding tax issues. Other countries have a fraction paid on tax compared to that of the UK.
When it comes down to it, there is no loyalty in football, its all about the money. Those who are looking for a massive pay day will look elsewhere as finacially its a safer bet.