Why is there a limit to the number of words sent by SMS?

Hello, the operator stipulates that the number of words in each short message is limited to 70 words. If it exceeds, send it by multiple words. 10 cents per message. If you write a 200-word message, send it in three articles, the first and second articles are 70 words each, the third article is 60 words, and the three articles cost 30 cents.