If they invested in themselves and it worked out for them, then it could work out better for them in the future and a lot sooner than what would have been possible, resulting in a higher position and greater rewards for someone of a higher status.
It was possible to find a way to climb higher much faster using that method, so the system could be abused in that way by someone who wished to climb higher right away upon joining.
If they were already highly capable upon joining, then they could use that method to rise through the rankings as quickly as possible using their skills.
If they were able to do that, then it would just prove that they were able to handle what would be required of them if their record showed it well enough.
If someone was using that method when they were too lacking, then they would soon hit their limit on how high they could rise.
The ranking upgrade tests were usually a way to judge whether they could be promoted or not.
