Why not? Obviously, Baidu knows that the copied things are not directly used for commercial purposes (perhaps indirectly). Baidu knows that it is just a platform for sharing knowledge and answering doubts. This is stipulated by the copyright law in China's criminal law. (I'm from Baidu)
There is a provision in the copyright law: Item 6 of Article 22 1 should be the legal provision you want.
Article 22 Under the following circumstances, a work may be used without permission and without payment to the copyright owner, but the name of the author and the title of the work shall be indicated, and other rights enjoyed by the copyright owner in accordance with this Law shall not be infringed:
(a) for personal study, research or appreciation of the use of other people's published works;
(2) appropriately quoting published works of others in works for the purpose of introducing and commenting on works or explaining problems;
(3) inevitably copying and quoting published works in newspapers, periodicals, radio stations, television stations and other media in order to report current news;
(4) Newspapers, periodicals, radio stations, television stations and other media publish or broadcast current affairs articles on political, economic and religious issues that have been published by other newspapers, periodicals, radio stations, television stations and other media, unless the author declares that they are not allowed to publish or broadcast;
(5) Newspapers, periodicals, radio stations, television stations and other media publish or broadcast speeches delivered at public meetings, unless the author declares that they are not allowed to publish or broadcast;
(6) Translating or reproducing a few published works for classroom teaching or scientific research in schools for use by teaching or scientific researchers, but not publishing them;
(seven) the use of published works by state organs within the reasonable scope of performing official duties;
(eight) libraries, archives, memorial halls, museums, art galleries, etc., in order to display or save the version, copy the works collected by the library;
(9) Performing published works for free, without charging fees to the public or paying remuneration to the performers;
(ten) copying, painting, photography and video recording of works of art set up or displayed in outdoor public places;
(eleven) China citizens, legal persons or other organizations written in Chinese and published in China;
(12) Published works are published in Braille.
The provisions of the preceding paragraph shall apply to restrictions on the rights of publishers, performers, producers of audio and video recordings, radio stations and television stations.
Article 23 When compiling and publishing textbooks for the implementation of the nine-year compulsory education and the national education plan, unless the author declares in advance that it is not allowed to use them, he may incorporate published works fragments, short stories, musical works or single works of art and photography into the textbooks without the permission of the copyright owner, but he shall be paid in accordance with the regulations. Marking the name of the author and the name of the work shall not infringe upon other rights enjoyed by the copyright owner in accordance with this Law.
The provisions of the preceding paragraph shall apply to restrictions on the rights of publishers, performers, producers of audio and video recordings, radio stations and television stations.