I don’t know the reason for your question.
I will answer you roughly in two aspects:
1. The better the calligraphy, the easier it may be to imitate. On the contrary, the worse the calligraphy, the harder it may be to imitate.
2. It is indeed difficult for everyone to imitate famous calligraphy. If you can fake it, your calligraphy skills must be better than his, otherwise you can see through it at a glance.
Calligraphy is a traditional culture, and its source comes from the Book of Changes. It has its practicality and functionality as well as its artistry. It seems to be mostly artistry now. Of course, pure artistic calligraphy is difficult to imitate because it is mixed with human nature, but for the Chinese, as long as it is a skill, it can be imitated!