What is the reason why a mobile phone can't send a multi-word message?

That's because your mobile phone doesn't support long messages, and you can only type 70 Chinese characters at most. It should be noted that even if your mobile phone supports several hundred words of long messages, when you send this long message, it will be automatically divided into several messages within 70 characters, and the second message after division will be less than 70 Chinese characters (for example, a message with just 140 Chinese characters is actually divided into three messages, and the first one is 70 characters). Therefore, a mobile phone message can only send 70 Chinese characters at most, and letters or other characters can exceed 70. If your text message is limited to 70 words, you are actually saving information for you.