It would be probably be the bittrex delisting policy "We encourage you to request relisting when you have completed and fully implemented the basic application for which you intend your token to be used and both the application and token can be used by the general public."

link: https://news.bitcoin.com/bittrex-delisting-policy-leaves-cryptocurrencies-cold/

but i wouldn't try listing in bittrex again cause they will certaintly be a bad exchange soon cause of certain legal regulations that they would be adding in the future, rise team should consider adding the coin in binance since is starting to be a good exchange