Disregarding sporadic successes; Holland and Portugal don't have a quality home base from where they can launch consistent successful attacks on Europe.
Weaker league = smaller audiences = less money = less buying power = less stars = a weaker league. A very, VERY difficult spiral to break through. It hasn't been done yet in modern times (since the Bosman arrest).
The holy grail of modern football is TV money (unless you're Russia - oligarchs). In the financial aspect of football, England has started an insane race that's spiraling out of control. If you fall back in this race, like Holland has, there's no coming back. Portugal is now following Holland's lead (Porto drawing serious parallels to the Ajax of the mid-1990s). If Italy is going to go down the same path, they're doomed. The point of no return is closer than many Italian football fans might think.
Italy's case is made worse by the fact Germany (extremely wealthy clubs & league) and Russia (oligarchs) are uneven competitors. Germany has always underperformed, its clubs are
among the richest in Europe. Russia is just too rich to remain 6th forever. Serie A has to come up with a new game plan fast or they'll be caught and overtaken.