Why do group text messages on Apple phones turn into multimedia messages?

How to handle text messages sent by Apple mobile phones that become MMS messages: When sending text messages, if there are too many words or content is entered in the subject bar of the message, the text messages will be converted into MMS messages.

The processing method is as follows: Go to "Settings" > "Message", select "Send and receive MMS messages" or "Show subject bar" to turn it off as needed. The processing method for sending group SMS is the same as sending a single message.

Note: Turning off the "Send and receive MMS" function will affect the iPhone's MMS sending and receiving function, please handle it as appropriate.