Simple Past vs. Past Perfect Continuous

[spider1413]

"For a couple more years, I (struggle) struggled through grammar and vocabulary lessons."
"I (stay) stayed with a host family for one month."

I have done a test today.I can`t understand why the correct verb form used in these sentences is Past Simple.

For me,it was clear that i should use Past Perfect Continuous,because it emphasizes the duration of these actions.
Besides, I always thought that prep. for cannot be used with Past Simple.

Thank you for your answers

[Raymott]

"For a couple more years, I (struggle) struggled through grammar and vocabulary lessons."
"I (stay) stayed with a host family for one month."

I have done a test today.I can`t understand why the correct verb form used in these sentences is Past Simple.

For me,it was clear that i should use Past Perfect Continuous,because it emphasizes the duration of these actions.

Besides, I always thought that prep. for cannot be used with Past Simple. Why would you think that?
"I lived in London for six years." Are you saying that you thought that was wrong? It's not.

Thank you for your answers

Let's be clear. You thought that the following was the right answer?:
"For a couple more years, I had been struggling through grammar and vocabulary lessons."
"I had been staying with a host family for one month."

These could be correct sentences, but there is no evidence for the need for the past perfect. Neither has two events in the past, which is the absolute requirement (necessary, but not sufficient) for past perfect (continuous or not).