Because people that go out and build their own don't think about added weight and airflow that could boggle the system down. I'm not saying you won't think about it but the average Joe could. I'd rather stick with products I know will last, already small enough, and has enough power to run what...
I'd rather have lighter devices for external use than heavier devices with built in power making the weight of it outweigh it's points to be more portable and compact. A single wire isn't going to kill a person to walk around with. We are getting extremely close but too much of a closed...
I almost bought a wireless hdmi kit but moonlight/sunshine combo still works pretty smoothly. Isp being down would be the only benefit of wireless hdmi.