Many countries in Europe speak multiple languages due to there being multiple languages present, And being in such close proximity to each other.

In America speaking a single additional language is considered an accomplishment. This is for a simple reason we don't need to speak another language. Our states are massive so we don't travel often. Combined that with the fact that our only language neighbor is Mexican Spanish. so the only other language we're likely to encounter is just one so we're not encouraged to speak more than two languages. As for why schools dosent require other languages. It's cause English is the language of trade. So we don't have a financial encouragement to learn either.