Here's why:
* Paraphrasing means putting someone else's ideas into your own words. You are summarizing or rephrasing the original text, not directly quoting it.
* Quotation marks are used to indicate that you are directly copying the exact wording of someone else. A paraphrase does not use the exact wording, so it doesn't need quotation marks.
However, you still need to cite your sources when you paraphrase! This is important to avoid plagiarism. You can cite the source using footnotes, endnotes, or parenthetical citations.