I was bringing in 3k a week, after cost. for most people that's pretty good money. however, as the above fake internet mom insinuated, most dope men have spending problems. The guys you're talking about, the street walking, dime rock sellers, are only part time. either they sell a bit to make a few extra coins, or they sell enough to pay for their own high.
Full time dealers who stay out of jail and know at least a handful of users have a hard time not making a decent living.