[wtmcc]

The traditional American Spanish classroom is probably at least 80% English, and students are in it perhaps 5 hours a week. = 1 hr/week total

Compare this with the experience of a Spanish native speaker dropped into first grade in America, and not knowing a word of English. They have school for 6 hours a day, every weekday. = 30 hr/week total

These are not comparable, even by volume.

When you account for the burden of code-switching among languages, and the disconnection from what interests them of what little Spanish the Americans hear, it’s even more obvious why we Americans don’t end up learning Spanish, and Hispanic immigrants who go to school in the US speak English with fluency and ease, even when they first encounter it only late in life.