Star Trek had its biggest TV audience when it was being watched by families
: syndicated repeats of TOS in the 70s, stripped five-nights-per-week in the early prime time timeslot, and then syndicated first-run TNG in the late 80s/early 90s.
As DS9, VOY and ENT slipped into later and later timeslots, so that wider demographic got narrower and narrower.
Interesting that when the 2009 movie came out, sales of boxed sets of all the previous ST series
went through the roof. CBS Home Video found it hard to keep the sets in stock for a while. The diehards already had them, of course. The family groups didn't, but the JJ movie made them hungry to find out about things they had missed.
Will some future Netflix system satisfy family viewing? I guess the biggest hurdle is that when something important will air once only, people organise their lives around that one event. (Similarly, a gala premiere night at the movies.) When the people are free to choose a viewing time of their own convenience, they don't ever get around to watching it together. (Looks at my own towering piles of unwatched DVDs and Blu-Rays.)
How to turn ST watching into "an event" again?