Earlier quoted context omitted.
Chinese is many times harder to learn than the other languages you mentioned for Native English speakers. It takes about 4 times as long as French and Spanish to become proficient. Given the amount of time kids spend on foreign languages in school, there's no way they're learning enough Mandarin to be useful. I took Mandarin as an undergrad, and I can understand more Spanish despite having never studied it.
You can absolutely learn enough Mandarin to be useful in 2 years of weekly classes. Source: That was my level when I went to China. I felt not at all ready, but then I discovered that my limited knowledge could get me quite far with a little effort.
Cramming for a few weeks before visiting a country is useful.
It takes the average fully trained foreign service officer who already speaks multiple languages about 2200 hours to become proficient. And this is 2200 hours at arguably the best language school in the world doing nothing but studying Chinese full time.
2 years of of Weekly classes is about 100 hours of class time.