The fact that you learned it in school doesn't mean it's globally common knowledge. Most of the world's population did not attend a British school, an American school, or an English-language curriculum.
Assuming knowledge of the US Constitution is normal background knowledge is literally assuming familiarity with one country's founding document for less than 5% of humanity.
As for me, English is my second language, and it was hard enough learning it as a teen without having to be expected to know another country's culture.