
Hi, there! I'm namihei from Japan.
I have posted the article in English to study English, so please correct my wrong English.
Today, I will share how to say ”Why not" in Japanese.
Let's get started!!
Why not is used for making a suggestion or expressing agreement, right?
I will share you with how to say "why not" in Japanese using the following sentences.
Ex.2 Do you want Japanese food tonight? Sure, why not.
In the case of the situation of Ex.1, why not is called "~したらどう?(~shitaradou)" in Japanese.
Let's take a look at the next sentence.

Sayuri
If you’re so unhappy, why not leave?
不満なら,帰ったらどう?
Fumannara, kaettara dou?
While, in the case of Ex.2, "why not" is called "もちろん(mochiron)" or "いいよ"(iiyo) in Japanese.
Let's take a look at the next sentence.

Sayuri
Do you want Japanese food tonight? Sure, why not.
今夜日本食食べたくない? もちろん,いいよ。
konnya nihonshoku dabetakunai? mochiron iiyo.
How about this article?
I would be honored if this article helped you learn Japanese.
Thank you for reading!!
/namihei