To Charlie, Gustavo had lost his value after he had successfully approached Bruce.
A Mexican drug lord who had lost his power and was imprisoned by the Americans on top of having a son who wanted to be killed had no practical value.
He would be useless unless Charlie got him out of jail and brought him back to Mexico to help him regain control of the Sanchez family, but that was even less cost-effective for Charlie.
Firstly, Gustavo was a notorious drug dealer whom Charlie did not want to