There are many steps to setting up a DNS seed, so it is next to impossible to determine why your attempt failed without having more knowledge of your setup.
But if you are trying to set up a DNS seed for an alt coin, then I would strongly suggest you use the generic-seeder to prevent having to muck around in the source code.
The generic-seeder is a clone of the original bitcoin-seeder app that aims to make it easy to run a seeder for virtually any blockchain network. The bitcoin-seeder was developed specifically for the bitcoin network only, and configuring it to work with a different blockchain network can be time-consuming and tedious at best. The generic-seeder overcomes this limitation by utilizing a configuration file that holds the data used to connect to a given blockchain, without having to edit the source code, and adds new features and a full setup tutorial as well.
Github repo: https://github.com/team-exor/generic-seeder
Step-by-step setup guide: https://github.com/team-exor/generic-seeder/blob/master/SETUP.md
Full disclosure: I am the author of the generic-seeder.