1. In the 20th century, Spain was ruled by a dictatorship, which turned away other countries -- whereas pop culture turned the world's attention towards America, Western Europe (especially Britain, France, and Germany), and Japan.
2. The other powerful European countries, such as Britain and France, seized their chance to take Spain's place as Spain lost its colonial possessions.
If only a more competent leader existed back then to challenge the other European empires and America, the Spanish would have still remained (or returned to being) a nation that is more well-known, instead of being eclipsed by other powers.