In satellite communication, we have the low noise amplifiers (LNA) and the low noise block converters (LNB) at the receiver on the dish. Since, we know an LNA will amplify the weakened satellite signal at the receiver without degrading the SNR value and the LNB will not only amplify the weakened signal, but also down convert it to lower frequencies.

Why the need for this additional circuitry at the user end? Which is the cheaper alternative, with regards also to other associated equipment specifically cabling?