ACM only makes sense when there is feedback between the client and the host. If there isn't, the only thing that can be checked is uplink success through self monitoring. Adaption for downlink quality at the client location is impossible without feedback. And even if there were feedback from the client, in the case of DTH there are multiple clients (millions) so the signal would have to be adapted for the poorest performing client, which is why ACM doesn't make sense in the concept of DTH. In the case of DTH there is no feedback from the client, so all the provider can can do is operate a non-adaptive, good-enough policy (fixed modulation and correction), and if one of the clients goes offline due to downlink quality (rainfade for example) that's tough luck.