Hi,
The goal of https://rules.sonarsource.com is to let people discover SonarSource offering in terms of static code analysis rules, and see which of SonarSource products implements those rules. There really is no plan to add any export capability there.
You haven’t explained why do you need to download the rules list in a CSV format, so it’s hard to give suggestions that would best fit your use-case. Feel free to clarify that.