The reasons are as follows:
First, ancient classical Chinese is concise, while modern Chinese has many repeated words. Ancient Chinese characters are condensed and there are very few heavy words, because the presence of heavy words will affect the rhythm of the article. But modern Chinese just repeats and repeats.
The second is the rhythm of writing. Calligraphy is connected with Chinese characters, music, diction, and the use of pens. This is more troublesome to talk about, because it all depends on Shenhui. The rhythm of writing, especially cursive writing, is similar to the rhythm of ancient articles. When we write now, we still know how to write sentences one by one. Do the ancients just randomly combine two words when writing? Of course not. The ancients would also recite silently in their minds when writing, and the rhythm was the key. Of course, there is no need to understand the melody and rhythm of ancient Chinese prose, but one thing is certain. Reading more ancient Chinese will be beneficial to improving your calligraphy skills.
The third is the personal level. Modern Chinese has many repetitive words, but it can still be written. In theory, the arrangement and combination of any words are arranged by people. If you don't write well, it must be your problem, not the article's problem. For example, if "的" appears five times, how can it be written beautifully? Most people can't write this character well, because ancient people rarely had this character, and the way to write this character can't be found in everyone's "character pool". This is a matter of personal level. Once you practice calligraphy to a certain level, you can master any content.