es fehlt- fehlen=to miss/to be missing- as in something is missing (the answer, some money, information...
verpassen=to miss - as in missing the train; "ich habe den Zug verpasst"-"I missed the train" http://www.dict.cc/?s=h%C3%A4ngen&play_first_audio=DE; also can be used for missing a person "ich vermisse dich"-"I miss you" http://www.dict.cc/?s=I+miss+you+a+lot%21
My guess would be because "lacking" and missing do not mean the same.
You can say "the answer is lacking" but it means that that the answer actually exists but lacks something. Such as not having good reasoning, or someone not showing their work in an answer to a math problem.
In contrast, " the answer is missing" means that the answer is not there at all. Not even in part or a bad one. As in "Die Antwort fehlt'
Ahhh, I have understood something strange. Let's elaborate . let's conjugate this verb "fehlen". The conjugation of this verb for first person (ich) is fehle. And this is pronounciation https://translate.google.de/m/translate?hl=de#en/de/fehle and for this word " viele" here is the pronounciation https://translate.google.de/m/translate?hl=de#en/de/viele . what is the difference in pronounciation. Can anyone has a good idea