Why does using an AT&T Star Service while on LTE temporarily switch you to 4G?

This question applies to phones on the AT&T network. I don’t know if the same happens on other networks. You're no doubt familiar with the AT&T Star Services codes one uses from the Phone app on an iPhone, such as *3282# to check data usage or *646# to check minute usage. Whenever I send one of those codes while on the LTE network, the connection switches to 4G and remains there until you get the information you requested (via SMS), and remains on 4G even after the SMS text is received. After anywhere from 20 to 60 seconds the connection automatically goes back to LTE. Any idea why this happens?