Exactly. Unless things have changed dramatically, one or two years of a foreign language is a requirement in high school, and there are more opportunities in lower K-12 these days from what I hear. However, you're right that this is not especially helpful without some immersion, and the practice of trading your kids to a foreign family for a year is far less common. Then, after K-12, opportunities to practice greatly diminish.

The German mother of a good friend moved to the US West coast when she was a young adult, married, and had my friend. She never lost her German accent. When I was in my early 20s, I had the opportunity to live and work in Germany for a couple of years, and when I came back, I was fairly fluent - enough to pass as a native from a "different region." I visited my friend when I returned, and tried to have a conversation with her mother in German; she sadly informed me that she had forgotten most of her German, and could no longer converse... there are few opportunities to speak in German on the West coast, and even native language skills attrophy if unused.

In a related annecdote, when I first returned to the states, I'd sometime fail to remember the English words for the odd thing, like "trash can." All I could remember was the German word for it.

All thay has gone away. Years later, I can barely hold basic conversations in German. Maybe some people have an ability to retain language skills without practice, but I believe it's far more common to lose fluency you once had.