When we want to show the reason why something happens, we can use 'why' or 'because.'

'Because' is mainly used to answer the questions that are asked by 'why.'

We can also use 'that is why' instead of 'because' as showed in the dialogue below:

As you can see in the example above, 'that is why' is used before the result and not before the reason.
We can also use 'why' after the noun 'reason' to express reason and result.

'Why' can be used as an interrogative adverb or relative adverb. 'Because,' however, is used as a conjunction.