There is a story around that this is because the OM requires 500 multi crew command hours for the PIC, so Bras FOs are not suitable and putting them in the right seat of the F100 also will not help them get an upgrade, therefore the only other option is external candidates. Do the "turboprop drivers from Skippers" have 500 multi crew command? If so then there is your answer.
Apparently its not the braz FO's that are getting looked over, they are happy to wait their turn for command and get the 500 Multi crew. Its the Braz captains that have been there for years and have been shafted by employing DE f100 drivers. apparently there has been 5 internal braz captains upgraded in the last 18 months with more than 15 DE f100 drivers in the last 6 months.