To answer your post:
This has nothing to do with excuses or perceived difficulty. It has everything to do with cost benefit analysis. When forcing a group of students to learn a language, usefulness vs difficulty is a valid concern.
The State Department estimates that it takes only around 600 hours of classroom instruction to learn Spanish, but 2200 hours for Mandarin (for a native English speaker). They also recommend that half of the hours learning Mandarin occur in country.
30 minutes a day for 13 years of school won't provide enough instruction for these kids to become proficient, but it could provide enough to become proficient in 2 category 1 languages.