I am learning how to use the form ために and found many examples were the particle の is inserted just before it. I don't understand why.
今度の面接のために、このスーツを買いました。 'I bought this suit for my upcoming interview.'
健康のために、毎朝に走っています。 'For my health, I go running every morning.'
別に彼のために作ったわけではない。 'It’s not like I made this for him.'
In all your examples the word before のために is a noun. The word ため is itself a noun and の is how you join two nouns together. So I don't think there is much reason to be surprised here.
Perhaps you also saw examples with verbs before ため but, as I'm sure you already know, verb phrases modify nouns directly so you would not expect to see の in these cases. Everything is consistent if you think of ため as noun (which it is).
