Affordable Connectivity Program Credit only be applied to internet or wireless but not both?

An agent from the ACP department told me that the ACP credit can only be applied to the internet or the wireless plan but not both. I don't understand why this would be the case. If you have $10 Access From AT&T Internet Plan, that leaves $20 of credit left that should be free to be applied to an existing wireless account. The internet department says they upgrade the internet plan to take advantage of the full $30 credit but most users don't need unlimited data or the speed increase on their internet. Comcast doesn't seem to have this issue with their $10 Internet essentials plan where the $30 ACP credit can be split between the Internet and the Xfinity Mobile account. If Comcast can apply their ACP credit to the Internet and Wireless portion of the bill simultaneously, there is no reason AT&T couldn't do the same.