The main reason behind a torrent file that doesn't even start downloading is the lack of seeders and peers. In other words, there is no one seeding that file, meaning there's no place where you can download it from. That's why it's very important that you have a look at the number of seeders and peers every time you start a new download.
Why is my PC noticeably slower when downloading a torrent Sep 16, 2013 Stop BitTorrent from Killing Your Internet Connection A slow to finish downloading game, movie or file from a torrent is not really a big problem. The biggest problem you’ll probably encounter is when someone else is on the network and your computer is downloading a torrent. 4 Ways to Bypasses ISP Torrent Throttling Allowing Faster
Jul 20, 2018 Why Some Torrents Download Slow? - AddictiveTips Jan 20, 2018
utorrent on WINDOWS 7-very SLOW download SPEEDS - Windows
qBittorrent download speed is really slow for me unless global upload rate limit box is checked off. Downloaded some fast Linux torrent files, and no matter what upload limit is set, download speed is over x2 slower than in no upload limit.