What determines what channels a cable company offers?
Charter Cable doesn’t offer the Sci Fi channel in my area, although they do in some others. I would presume that it costs the same to offer it in my area as in those nearby, and that they have a satellite dish aimed at W5. Do they need a dish aimed at W5 for each feed and just don’t have one available for Sci Fi?
It’s probably just an infrastructure limitation.
If their headend facility is old and can only support say, 50 channels, or their downstream installed base of hundreds of miles of cable and hundreds of in-line amplifiers can only handle up to a certain frequency, they may be stuck - after bringing you all of the “must carry” local channels, and the premium channels that people pay extra for, such as HBO or Showtime, they might not have space for that one more channel.
At that point, one can only hope that they’ve based their selections on what to carry or not carry on responses from their customers. So call them up and tell them you want Sci Fi, err, SyFy.
There was once a time, perhaps 2001, when Charter gave us Comedy Central with our package. We moved across the street and couldn’t get it without paying more for the “same” package.
I told the guy it was a dealbreaker, but since there is no more Battlestar Galactica, SyFy fellates with great allacrity.
We are in a rural area, and I cannot help but wonder if they bought Falcon cable, which consisted of three 12’ dishes, a bunch of antennas on a tower, a house behind a convenience store and as far as I know the existing cable runs in the area. They were why I got C Band and added Dish Network. 
Ah, they have the (n)ever-popular 12-channel headend. 
Joking aside, they probably do have some severe technological limitations compared to the newer systems that also bring goodies like high-speed internet, XM radio channels and 300-odd channels of video on demand.
Sometimes equipment does factor into decisions, but often it’s just agreements.
For instance, in you case you aren’t aware, TV statons are all assgined a market by Nielsen. The FCC uses Nielsen’s markets for its purposes. Note Nielsen markets are defined by Nielsen NOT the FCC, but the FCC uses them anyway.
A TV station has two options when it comes to cable TV. They can demand the cable company carry their signal, and if they do that, the cable company gets to carry the signal for free. This is called “must carry,” and is usually involked by TV stations with weak signals or that carry things like all infomercials.
The TV station can also demand “payment,” for carriage of its signals. Now here’s the thing, the “payment,” doesn’t have to be money. For instance, a small independent channel on over the air (OTA) channel 69 may say, “the cable company’s payment is placing our UHF channel on channel 6.” You see its getting “paid,” be getting a better channel placement.
Now some stations are owned by powerful companies. For this example we’ll pick on FOX. WFLD-TV in Chicago is owned by FOX, so it could say “You know what if you want to carry our FOX programming you have to carry all the cable channels owned by FOX.” Now since FOX is currently the #1 Network they have the most pull. Then say WBBM-TV in Chicago, owned by CBS says “If you want CBS signal you have to carry all the cable channels owned by CBS”
So you see, this is how negotiations start and they can give you channels and have channels taken away from cable companies. After all the deals are done with the OTA channels, then whatever is left over the cable companies can fill up.
And the cable companies can play hardball, too. You want ESPN? Then you’ll have to take ESPN2 or ESPN News. You want CNN? Then you have to take Headline News, etc.
The latest battlefield is HDTV. The OTA stations are demanding some sort of compensation from the cable companies for the privilege of carrying their hi-def signals instead of the standard digital signal. Maybe that compensation comes in the form of also carrying one of the OTA station’s digital subchannels. More stations, but no more capacity on the cable line.