Emigration was certainly a common phenomenon in Spanish history, as it was in the history of the Italian peninsula, England, France, and Portugal. And, as books like Margarita Cervantes-Rodriguez' International Migration in Cuba point out, massive numbers of gallegos, catalanes, asturianos, canarios, and castellanos came to Cuba and other parts of the Americas.

They often faced the same kinds of social pressures which spurred immigrants from other parts of Europe, such as the lack of economic opportunity (Raymond Carr: Spain, 1808-1975, on the case of Galicia see pp. 8-11, 414).

They also appeared to have come to the Americas in roughly the same volume as immigrants from other European countries. According to the study by Consuelo Naranjo Orovio, Spanish emigration to the Americas numbered about 3,297,312 between 1882-1930, of which 1,118,968 went to Cuba. Hundreds of thousands more had come in the preceding decades as well. ("Analisis Cuantitativo", in Historia general de la emigración española a Iberoamérica, pp. 177-200, as cited by Margarita Cervantes-Rodríguez: Idem, p. 77)

Some factors that likely influenced the lack of prolific immigration to the US were the strong nativist (and often anti-Catholic) sentiment in much of the US as well as the plentiful opportunities available in areas which were culturally closer to Spain, such as Cuba.

Cuba was still a Spanish colony at the time, had a booming economy thanks to sugar plantations (and to a lesser extent coffee and other tropical goods). Even after Cuba and Puerto Rico were lost in 1898, Spanish immigrants in the Americas maintained social and kinship networks with their homeland, sending an estimated 1.1 billion pesetas between 1906-1910 in remmitances (idem, p. 96)

Prospective immigrants looking to leave Spain could count on not having to learn a new language, mutual aid societies (usually based on an immigrant's origins within Spain, such as Asturias, Galicia, Catalonia, etc.), a lack of hostility on the basis of their religion, and economic opportunities which were often at least as good as (or almost as good as) what they might find in the USA.

Territorial empire does not always determine where people choose to immigrate to. If that were the case, then the United States, mostly lacking one, would not have seen immigration. As it turned out most of the immigrants from Spain went to parts of the former Spanish empire which were experiencing massive economic expansion at the same time as the united states. In particular places like Argentina, which in the early twentieth century had living standards which rivalled european ones. This was partially due to government sponsorship -- they removed the natives and opened up massive amounts of new land for settlers. Argentina had the second highest amount of immigrants after the United States at 6.6 million. Of which 1.5 million were Spanish and 1.4 million were Italian. As for the French, most of them went to Algeria. It had most of the advantages of being in France, it was counted as a metropolitan departement, with all the advantages of white hegemony like commercial opportunities and new land extorted from the native population while being close to France. So in 1926 15.2% of the population of Algeria was of French extraction. European Frenchmen also went in relatively large numbers to France's remaining Caribbean colonies like Guadeloupe and Martinique.