setNextRequest just sets the request that will run after all of the code in the tests tab has been completed.
This means, the “for loop” will run to its completion before the next request is run.
Therefore, the last entry in the for loop will always be what is set in the “prompt” collection variable.
See the following for an example of looping through an array, which utilises a pre-request script to set the current variable, and the tests tab to control the loop.
Simulating 100 users using Pre-Request and Tests - 
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