Why are the majority of CHANNELS on PMS and on ROKU simply NOT WORKING - no content or server etc.

I have two ROKUs, ..Neither one dispenses content reliably or at all. I sometimes get
FOX NEWS and NY Times..but no PANDORA, no HISTORY, no HGTV and on and on.
One would think, as good as PLEX is, that all this would be cleared up completely. The
boards are choppy and all over the map in advice..
So..what say you PLEX?
Rogelio