I believe people whop mostly spend money in Cartel Market is the lowest level casual player who is attached to Star Wars concept/brand and prefer to play only easiest content.
I don't think this is correct. In my experience, there are people at all levels (of clearing PVE group content, say, as that's what this thread is about) who spend lots on the CM, and people at all levels who steer clear.
I don't know the percentages of different populations, but I'd assume anyone who with any regularity clears any level of op would be retained longer with more ops. What makes business sense, I admit I don't know, but I'd guess there's a sizable population who, if you removed the various things to work on / aspire to in terms of clearing content (and this is varied and different for players at different pve-group-content levels), would no longer stick around.