Why are the above sentences considered as hypothetical situations?
Language is very flexible, and you're free to make statements that are either hypothetical or not.
"We will go to the restaurant" is a confident-sounding prediction of the future.
"The restaurant is expensive" sounds like a basic, correct statement.
It's not required to add "would". If you do, then the sentence takes on a uncertain, unreal quality.
"The restaurant would be too expensive..."
Now you are implying that you won't go to the restaurant. Going to the restaurant becomes an imagined possibility.
Refusal (with the negative). "E.g. Jack wouldn't help you, even if you begged him."
Reviewing that specific sentence, brings to mind the question: "Is it certain that you will ask Jack for help?"
If definitely yes, you may say:
"Jack won't help you."
"Jack won't help you, when you go to ask him."
However, if it's uncertain that you're going to ask him, then the entire scenario is hypothetical, imaginary, and merely possible. Then we might say:
"He would help you, if you asked him. But you might not ask him."
Let's consider some alternatives from the perspective of grammar:
"Jack won't help you, even if you begged him." (* not recommended)
"begged" is past tense, indicating a conditional mood, and so to be consistent, the whole expression should be conditional, and "would" probably sounds better.
"Jack won't help you, even if you beg him."
This is probably OK. In simple English you may just use simple grammatical constructions.