Why can't Apple use the 4g network for its own wallet?

Because the "data permission" of "wallet" is closed, just open it in "cellular mobile data".

Take the iPhone8 mobile phone as an example, the specific operation is as follows:

First, open "Settings" on the phone desktop.

2. Open "Settings", find the column of "Cellular Mobile Data", and click Next.

3. Finally, find the "wallet" column on the "Cellular Mobile Data" page, and click the "button" on the right to open "Data Permission" to complete the operation.