Is なんでこれ the most common way of saying "why is this?"

Question

Let's say I'm asking a question here on Stack Exchange, and finish the question by saying "Why is this?"

Is なんでこれ the most common way of saying this? If not, what's the best alternative?

Answer 1

Direct translations are usually not a good idea, and in general it's best not to ask "how do I say this in Japanese?" but "what is the natural thing to say in Japanese that is closest to what I want?".

なんでこれ is definitely not what you want; it's difficult for me to articulate, but it sounds like you're asking "why this specific thing among other possible things that could have been chosen?". Somewhat like English's "why this?" (as opposed to that).

The most common structure I see for this kind of question is simply なんで？ or なんでですか？, in something like

アメリカと日本の平均体重は全く違います。なんでですか。

If you really want to emphasize why is this, you can also explicitly say これはなんでですか。