Acquisition vs. learning
Many English language learners are told that language acquisition vs. language learning is more effective. That’s why most people believe immersion is guaranteed to teach you a language. Immersion is essentially acquisition in its purest form. You rely on the environment to provide input and language acquisition just happens magically with repeat exposure to the target language.
Enrolling in a language class entails deliberate learning vs. language acquisition from your surroundings. Sure, some language acquisition will happen as a by-product (posters on the classroom walls, the teacher’s repeated use of a certain phrase) but most language will be learned through memorization and direct study.