Galdós's lack of fame outside of the Spanish-speaking world is often attributed to a nasty smear campaign launched by his compatriots when rumors began that the writer was going to be nominated for the Nobel Prize. I find this explanation to be quite silly. It would have made sense to talk about the smear campaign as the main cause of Galdós's relative obscurity if it weren't for the fact that every single Spanish writer (with the exception of Cervantes, Lope de Vega and, marginally, Calderón) has suffered the same fate. Take, for example, Clarin's La Regenta (Penguin Classics). (And I mean it literally as well as figuratively: do absolutely give yourself the joy of reading this fantastic novel. If you haven't read La Regenta (Penguin Classics), it is my opinion that you are pretty much wasting your time reading anything else.) Nobody has written a better novel since Cervantes, yet Clarin, its genius author, is as unknown (or more) as Galdós.
I hope that by now I have been able to awaken your curiosity as to the reasons behind this obstinate refusal by the entire world to notice achievements by great writers from Spain. Literature, though, is far from being the only area where Spain has been marginalized. Take any book on European history, art, politics, economy, demographic trends, whatever. In the absolute majority of cases, there won't be a chapter on Spain. I've been tracking such books for over a decade now, and, for the most part, Spain is noticeable by its absence.
So what happened to Spain? Why is this country being constantly snubbed, perennially left behind, eternally marginalized?
Between 1492 and 1898, Spain was an empire. In the XVIth and the first half of the XVIIth centuries it was the greatest, the most powerful and the most feared empire in the world. Spain's hegemony in terms of politics, economy, culture, art was undisputable. The Spanish Empire didn't rest there, of course. It used all of its vast resources to invade everybody around in order to impose its own religion. Eventually, Spain's endless religious wars destroyed its economy and led to a gradual crumbling down of the imperial edifice. By the end of the XVIIth century, Spain became very familiar with what it meant to be an empire in decline. By the 1820ies, Spain lost most of its colonies. In 1898, the sad, pathetic remnants of the Spanish Empire lost the last small colonies to an emerging imperial power: the United States.
People remember, though. The atrocities perpetrated by Spain in the New World were retold and exaggerated by those who resented Spain's religious wars and constant attempts to mess with its neighbors. This horrible reputation that keeps following Spain around like a bad smell is called "The Black Legend of Spain." Of course, there hasn't been any Spanish Empire for a long time. And only historians and Hispanists remember Spain's hegemony. Still, a bad rep is impossible to live down. And Benito Pérez Galdós - as well as everybody who could have enjoyed his books if they knew of their existence - keeps paying for the Empire's sins.
So you see how this works? Messing with other people's business, starting "holy" wars, exploiting others for the sake of the Empire is a lot of fun while it lasts. But you always get to pay for it. And pay for it some more. Is it really worth it?