The search engine is designed to index and rank sites with a preference for high-quality resources that provide meaningful information for users.
Sites can't be considered high quality if they try to manipulate the search engine with search spam or pose a threat to users (lead to a computer virus or downloading unwanted software or files, and so on). Such sites are restricted in search results using special algorithms. These restrictions can affect the site's indexing, ranking, and TIC.
In the Security and violations section in Yandex.Webmaster, you can check the security of your site and find out whether any restrictions have been placed on it.