Why does the number of short messages stipulate 70 words each?

Mobile phone operators (not related to mobile phones) only provide 70 Chinese characters (including spaces and punctuation marks) per message.

The difference is that some mobile phones support multi-page information, while others do not. No matter how many Chinese characters are entered into your mobile phone, the supported mobile phones will be automatically sent in multiple pages, and finally each message has only 70 Chinese characters.

MMS does not have this restriction.