Present Perfect - Past Simple question

Hey,

I still sometimes get confused with the present perfect and past simple.

For example this two sentences:

I wrote: The reason I have quit my job was that the salary was too low.
The sentence in the soloution says: The reason I quit my job was that the salary was too low.

I have choosen the present perfect, because he has quit is job. => He doesn't have this job anymore in the present.
So it has a present effect = present perfect.

Why is the past simple used in the solution?

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Another example:

Soloution: The results of the examination were released this week.
I wrote: The results of the examination have been released this week.

I thought this week was a signal word to use the present perfect. Why is the past simple used in this sentence?
Might it be because the action of releasing is finished? The results can't be released again this week?

Any help is very much appreciated. Thank you!