Why not? is a strange and wonderful expression. Here is its entry on the Cambridge Dictionary site:
used to make a suggestion or to express agreement:
Why not use my car? You'll fit more in.
‘Let's go out for Italian tonight.’ ‘Yes, why not?’
The first example is making a suggestion, and the second expressing agreement. Latin too has an expression that does this, but it isn’t why not? A literal translation of why not? would be cur non? As in, cur in Italia non habitas? Why do you not live in Italy? So, you might use cur non? like this: ego in Italia non habito? I do not live in Italy. cur non? Why not? Which is great if you want to know why I do not live it Italy, but terrible for making a suggestion or expressing agreement.
The expression we need is quid ni? quid ni? is constructed from two words; quid? what? and ni. I’m not even sure what to suggest as a literal meaning, but here is how to use it.
quid ni in Italia habites*? pulcherrima est! Why not live in Italy? It’s very beautiful!
visne mecum in Italia habitare? Do you want to live with me in Italy? quid ni? Sure, why not.
*By the way, habites is Present Subjunctive.
This man, meanwhile, (more or less known to you) is waiting for his associate Ravena. Perhaps you now would like to find out his name. Sure, why not? His name is Frank.