I'd say there's a few factors. Coke is a stimulant, weed is a depressant (in that it relaxes), so its effects are more "positive" or "productive" to the user.
Weed is relatively affordable compared to coke, so coke comes out a bit more "high-class" (obviously an argument can be made here in that skag is the most expensive of all and would be high-class by that standard).
Coke doesn't smell or leave an obvious trace.
And, of course, it's normalised in the friend/work group. I know people who use daily who don't consider themselves addicts because it's "just a bump". If everyone around you is doing "just a bump" then you're higher than those stoners who smoke constantly sure you can smell it off them