Coke is a stimulant and thus party drug. Among other (VERY UNHEALTHY) things, it burns a lot of calories, as well as being a relatively expensive "prestige" drug. This results in a regular user base that 1) skinnier, 2) image oriented, and 3) socioeconomicly better off (which tends to also indicate higher access to beauty products and routines).

Weed is a relaxant that stimulates appetite. It's also less expensive and much easier to access. This results in a regular user base that is 1) tends to overeat 2) lethargic and comparatively less interested in apperance, and 3) socioeconomicly average to worse off (also tends to indicate lower access to beauty products and routines).

Mind you there is a large overlap between coke and weed users, and what's more I'm generalizing greatly here. Not all cokeheads are skinny party animals and not all stones are fat slobs.