Short messages are generally limited to about 70 Chinese characters, but why are there far more than 70 Chinese characters?

Short messages with 70 characters are charged, and those with more than 70 characters to 140 characters are charged according to the second information fee, and so on, which does not mean that a short message can only be sent with 70 characters. Usually you see a short message of more than 70 words, which looks like one, but it is actually a long short message, and it is still charged according to 70 words.