Distributors do one job: they put your music on the streaming platforms. What they charge for it takes three different shapes, and the shape matters more than the sticker price, because they fail you in different ways.
You pay once a year and keep your royalties. Cheap in a good year and quietly dangerous in a bad one: stop paying and the releases come down, which means a catalogue you built over years rests on a renewal you have to keep affording. Worth it if you release often. Worth watching if you do not.
No upfront cost, and a cut of everything forever. It reads as the safe option because nothing leaves your pocket on day one. On a release that does nothing, it costs you nothing, which is most releases. On the one that works, it is the most expensive option you could have chosen, and you cannot change your mind retroactively.
Pay per single or album, keep everything after. Predictable, and it suits someone with a small number of releases they intend to keep up forever.
Distribution gets your music onto a platform. It does not get anybody to listen to it, and it is not a sales channel: a distributor cannot sell your album to a fan, only make it streamable. That is why distribution and direct sales are not alternatives to each other. One is shelf space and the other is a till.
Most distributors price in dollars and pay out in dollars, so a South African artist pays a conversion going in and takes another coming out, on top of the fee itself. It is small on each transaction and it is not small over a year.