First of all, one has to understand that requests for documents are just appeals to authors to put the full-text online for everybody or to send it to you privately. Many authors do not wish to reply or are not able or are not allowed to provide full-texts, or they are not active in ResearchGate or are not members of RG - note that your requests reach the authors only when they are members. I recommend to read also the answers to this question:

https://www.researchgate.net/post/What_is_the_average_response_time_for_a_full_paper_request

https://www.researchgate.net/post/Publication-Request-Reply

https://www.researchgate.net/post/What-happens-to-a-request-when-you-dont-have-a-digital-copy-of-the-paper

https://www.researchgate.net/post/I_requested_a_few_articles_and_have_not_received_any_of_them

https://www.researchgate.net/post/Text_requests_for_my_publications

https://www.researchgate.net/post/How_to_open_research_papers_which_are_not_accessible

https://www.researchgate.net/post/Requesting_copies_of_chapters_or_a_full_book

https://www.researchgate.net/post/Why_would_some_scientists_prefer_not_to_share_their_hardly_accessible_publications_with_others

https://www.researchgate.net/post/Why_people_are_not_posting_their_full_research_publications