Some music distribution services only charge a one-time fee for publishing a release. But that's where the work starts: storage costs, settlements, accounting, support, technical updates and further development of the service – this continually costs money.
So if a music distribution service only charges once for theoretically "1,000 years of service", this is very untrustworthy. This distributor finances itself necessarily only by gaining new customers, not by actual expenses. When it doesn't have new customers anymore, you have a problem.
Other music distribution services charge annual fees for each release. But the more releases you have, the more you have to pay each year.
We've found the best solution: You pay a flat fee and get new releases every year. You can choose how many releases you need.