Loaded: loaded (/lib/systemd/system/mongod.service; disabled; vendor preset: enabled)
This is disabled because it has been explicitly disabled. To enable the systemd unit sudo systemctl enable mongod
But it it not the reason mongod is stopping.
Main PID: 586388 (code=exited, status=1/FAILURE)
For the cause of this look in either the systemd log journalctl -u mongod or the mongod logs, by default /var/log/mongodb/mongod.log