It can be more factors such as bad content on your site, you are using wrong anchors .. but most likely its a bad PBN site. First you need a top quality domain even if you have to spend $500+ for 1 domain, then you need at least 50 or more relevant niche articles and let the site age 6+ months. Once it start getting traffic it will look like a real website which should be your goal! Then when adding keywords don't use only exact match, brand keywords are enough if topics are relevant on pbn and main site you want to rank. If it still doesn't go up then check some other things that you are probably doing bad. Also, if you publish article and it doesnt even get in top 50 without any links, then your domain have no strenght at all or content very bad, or keywords simply too hard and you have tough competition.