I'm not American but is there a channel in that option that has low rating compared to the big ones? I'll give you an example.
Our main channels here are BBC1/2,ITV,Channel 4 and Channel 5. We have other smaller channels that you can only get digitally or cable. But their ratings is very low.
A good show for BBC1 will get 5-9+ million viewers. The other main channels can expect lower but generally above a 1 million viewers. Sky One (the Premier Digital channel) gets around 800,000 viewers for a good show.
If we want Trek to come back and be successful for 7 years we should expect to set our sights lower. I'm just looking over at the ratings for Enterprise. In the last season the average rating was 3. That is something Stargate never got and that show lasted to long for it's own good.
Why not put the next Trek show in a channel/network what ever you call it in America and make in in such a way that a rating of 1.5 is ok.
Here is a rough ranking of those channels by size CBS > CW > SyFy > Spike > Showtime
CW is roughly the size of UPN(the network VOY and ENT were on). The problem with SyFy, Spike, and Showtime is that they are all on cable and are available to much fewer viewers. Also because they got a smaller audience SyFy and Spike have less money to spend on each episode. That's why Enterprise was able to go to alien looking worlds while SG1 always visits the pacific north west(the same type of forest in every episode).
Showtime is considered a premium channel. People pay $5-$15/month to get the channel. As a result there are a lot fewer viewers, but there is a larger budget because the viewers pay more. Also, because people chose to subscribe to Showtime it is allowed to (and quite often does) include adult content. The SG1 pilot is a good example. There is full frontal female nudity. It doesn't really fit with the show, but Showtime thinks its viewers expect nudity, so it makes sure its shows have nudity.
So basically the lower tier you go, the fewer viewers you need to survive, but the cheaper the show needs to be also. Unless you go the premium route which can survive with a higher budget and fewer viewers but results in a very different show from what previous Trek has been.
I hope that explains the issues involved to foreign readers.