Why can text messages write so few words?

The number of messages written depends on the mobile phone. Some mobile phones can write more words, while others can write less words. But no matter how many words a mobile phone can write, the charge is the same. The charge for sending short messages is 70 words each. Some mobile phones can write hundreds of words, some thousands of words, but when they are sent, they will still be divided into several pieces according to 70 words, so the money collected is not a text message.