beside about trading volume usually exchanges team look at project developtment progress. If after several months or year there is no important developtment exchanges will warn dev team first before decided to delist them. If any die project token still in market it could harmed investors , so its good prevention and protection step from exchanges to their users.
Actually the effect of decreasing trading volume is because the impact of project development has decreased so the community has been wary of selling before the project dies, I think exchanges should implement new regulations to open reports on projects that are not eligible to be traded for immediate delisting because it will harm investors and traders.
Less volume transaction on daily day just remaining with big and potential exchange only for delisting some coins or token but not happening with small exchange like Hotbit or LBANK. Actually with Binance exchange all coins have reach higher volume transaction and there have minimum volume on daily days, but I saw on Hotbit and LBANK without any buy order some coins keep exist for listing and not anything happen delist on exchange although without any interested from investor to but that coins without have buy order.