There are more than a couple of reasons while the comparison between Germans learning Spanish and Americans learning Spanish is a poor one. (Much less a comparison with Brazilian Portuguese)
1. The distance. Most of the US is actually quite far away from Mexico. As you get closer to the border (Texas, California, Arizona, New Mexico) the rate at which non-hispanics speak Spanish rises considerably.
2. The economic and social relations between the US and Mexico are nothing like those between Spain and Germany. If I'm German, I can learn Spanish, move there, find work (okay, the example works better the other way around), and live with a minimum of hassle. It's another stable, developed country.
In contrast, parts of Mexico are almost literally war-zones (Juárez et. al.), and gaining a work visa, finding employment, etc is quite difficult, and even then it will be a dramatically different standard of living.
1. The distance. Most of the US is actually quite far away from Mexico. As you get closer to the border (Texas, California, Arizona, New Mexico) the rate at which non-hispanics speak Spanish rises considerably.
2. The economic and social relations between the US and Mexico are nothing like those between Spain and Germany. If I'm German, I can learn Spanish, move there, find work (okay, the example works better the other way around), and live with a minimum of hassle. It's another stable, developed country.
In contrast, parts of Mexico are almost literally war-zones (Juárez et. al.), and gaining a work visa, finding employment, etc is quite difficult, and even then it will be a dramatically different standard of living.