In Spain, only a few options to study medicine in English can mean its “Private Universities,” with quite expensive tuition fee and living costs, especially considering their major locations within Iberian peninsula.
Therefore, it is more favorable option to study medicine in Spanish, especially if you are from those “Spanish-spoken” states of the US, not to mention the majority of South American nations. Still, you also need to consider there has been a long-chain of Spanish medical students studying in Hungary, Czech Republic, Poland, and Italy as a proof of their preference over Spanish medical universities, seemingly.
Furthermore, many of these “English” programs DO require their students to have B1 or higher level of Spanish language after the first 2 years at the medical universities. As a result, it is NOT really a popular among those “non-Spanish speakers.” What is more critical is that many of these English programs are actually located in “Catalonia” region, where people speak somewhat “different” language, which is “Catalan.” Again, it is even harder to imagine some foreign students start their medical school “in English at the beginning” and then continue to study “in Catalan,” which is still different from Spanish.