There are a few reasons why text messages might not show the caller's name even if the phone can display the caller's name for incoming calls.
First, text messages and phone calls are handled differently by the phone's operating system. While incoming calls are routed through the phone's cellular network, text messages are sent through a different network, such as a cellular data network or a Wi-Fi network. As a result, the phone's operating system may have different capabilities for identifying the sender of a text message compared to an incoming call.
Second, text messages are typically sent from a short code or a long number rather than a traditional phone number. These types of numbers are not typically associated with a specific person or organization, so it can be difficult for the phone to identify the sender of a text message based on the number alone.
Finally, Phone companies do not have access to the sender's name for the text messages unless that person has added their name to their phone contacts and shared that contact with the phone company.
So, in short, text messages and phone calls are handled differently and have different ways of identifying the sender, which is why your phone might be able to show the caller's name for an incoming call but not for a text message.