Jose Ortega y Gasset was a relative of mine, and I asked this as a kid. What I was told (by my grandmother, his niece) is that it is sometimes done when there's a weirdness in the combination of the two last names that would make it ambiguous, such as someone who has a compound first name like Jose-Maria that makes it harder to tell where a first name/last name breaks, or in this case, where it results in a repeated sound (ga-ga) that feels weird to say. But I have not found any corroboration of this online.