Well look at it this way....
1. CM offers extra items, maybe for fluff as some people say, or maybe because people want to get in the "spirit" of things which IMHO is what a star wars mmo is all about. You're doing role play without knowing it
2. If no one bought from the cartel market, BW has less income and you might see less frequent updates. For BW its still a business and you are helping people, yes indeed PEOPLE, make a living. They do pretty great bringing us new things every update. I know some people have the attention span of a fly and want everything now and not tomorrow, but there new things to try in every update.
3. If no one bought from the cartel market, those items wouldn't show up on the GTN
4. Maybe the reason why the cartel packs are gambling sets, is so that people end up with stuff they have double or don't want and they would actually sell them on. If you could buy exactly what you wanted from the cartel market without a bit of a gamble, would any items even show up on the GTN?
5. If you compare the price of a subscription and a few cartel coins (or even a lot) to other online communities, we're pretty good off. Just compare it to other pass-times... go to the pub, go play some kind of sports, laser games, paintball etc to name a few and for a few hours you've outspent your hours and hours of fun is SWTOR.