Remember RA couldn't force players to go a team, it had to all be agreed by the players, and mostly there would have been no salary/extra payments on the table to convince players that (eg) Canberra was a better option than Sydney.
RA were in control of contracting at the Tahs too, but not at the Brumbies, so could make the decisions they needed to clear the spaces for the Rebels players where they needed to. RA also can't grant more money to one Super Rugby licence holder over another, so couldn't do financial deals that way either