Biden and his administration doesn't want to just keep the U.S.-Mexico border open. It wants the borders of Latin American to remain open as well. Instead of seizing an opportunity to stop the flow of illegal immigration through Central America, the Biden administration is encouraging more.
Blinken supposedly asking Obrador to stop the flow in Mexico is pure theater for the stupid.
Biden could stop it now by closing the border and sending armed troops with shoot to kill orders.