I was surprised to discover that seasons 1-5 of "Disappeared" on ID (Investigation Discovery) channel are not available On Demand. This is particularly troubling considering the purpose of the show is to raise awareness of/draw attention to missing or abducted people. Thus there is a compelling public interest in ensuring all past episodes remain available/accessible to as wide an audience (i.e. potential witnesses) as humanly possible.
Comcast isn't responsible for pulling the missing seasons. That falls on ID. Comcast can only provide what the networks provides to them.