Because if you copy someone else's work and use it for profit, and the amount of illegal income obtained from this work is relatively large, then this time constitutes a crime of copyright infringement, which is a serious infringement of others' copyright, so you may be sentenced.

Plagiarism refers to the act of stealing or modifying other people's works for your own use, completely or partially copying other people's works in the same way, or changing their form or content to some extent.