I took three years of Spanish and got an A every semester. Even when it was still fresh in my mind, I was nowhere near able to hold even a very simple conversation. And now just a few years later it's all totally gone from my brain.
My mother's native language is Spanish and she never taught me, which I resent her for. But I still find it incredible how shitty my public school education in Spanish was. We really should be teaching kids a second language from kindergarten up.
Honestly it's just really hard to do in the classroom. It's not really a "subject" that you can sit down and learn through lectures and tests, it's a skill you need to actively train your brain for for an extended period of time through real-world practice. 20 kids sitting down while a teacher instructs them isn't going to be effective for most people to learn a new language