You know how on CSI they can zoom in on a 640x480 video camera and see the filed-off serial number on a gun? Sending lots of information over an AC power line is like that. There are many basic electromagnetic hurdles, many of them quite intractable. You have the issues of bandwidth over bare wires, bandwith through transformers, all the noise-supression capacitors across the power line, line noise from light-dimmers, fluourescent tubes, dozens of nearby switching-mode power supplies, lightning, salt on power-line insulators, corona on high-voltage lines, power-factor-compensated switching-mode power supplies that switch all through the AC cycle, LED lamps, streetlights, light-switches, brushed and brushless electric motors, illegal transmission and interference with amateur, land-mobile, radio-telescope and CB, and more.