1. There is no 301 redirect to the main version of the site in the search ( i.e. there is no redirection from http to https, or to the domain from www to without www). As a result, the site duplicates in the search and the result is a decrease in positions.
2. The filter pages on the site are not hidden from indexing by search robots. Countless similar pages overload the site and create duplicates, again lowering the position.
3. Not configured region in the Webmaster for regional sites. Sites with the specified region will be ranked higher, bypassing even the best site for optimization.
4. The slow speed of the site reduces the position.
5.There is no mobile version. Most users have already left in and the site without the mobile version will have a weaker position.
6. Duplicate content. It can be either on pagination pages in the catalog, or just copied text of products, for example.
7. Copying content from another site. Even if it's just a description of the products. So what if everyone does that? Why should a search engine show sites
10. Non-compliance with the H1 - H6 header tag hierarchy. Only well-structured content is appreciated by users and is given out by search engines in high positions.