English -ed is mandatory for describing past events. Mandarin 了 is not. It may be true that the sentence is more natural with 了 (I don't know, it's not my native language) but the comparison is inaccurate.
In questions, “了” is very rarely used in any of the dialects of Chinese. It is not always necessary to mention that the sentence has a tense generally...("tense" as I stated for English speakers, as in Chinese there is no such concept of tenses).