Would that be because they dont have enough bandwidth for customers let alone to spare for that ?
Not necessarily as any traffic locally would be free of the restrictions of the rest of the network,
just that the server will probably be used for other things too... When I used another server to download from it the speed was around 30Mbits...
So if theres 10 people doing speedtests from the Karoo speedtest server it would show a poor result.