A few things not mentioned:
(1) Whenever you see a quote in which the sentenced offender "writes" they're talking about Corrlinks. The person "writing" is sitting at a terminal that users of PINE would find familiar, paying 5 cents per minute to read and compose. Prisoners, of course, earn between 8 and 25 cents an hour doing things like "swabbing out dumpsters" and that 8 to 25 cents per hour also has to pay for things like $2/packet tuna fish. Thus, prisoners require outside money from those not incarcerated in order to regain a little humanity (if that's what instant coffee is) and the incarcerated economy functions as a way to tax the loved ones of the prisoner - all proceeds to private corporations, of course.
(2) the actual "drug dealers" are dudes in their late teens and early 20s up from Mexico at $300 a week. The Nayarit cartels have so streamlined things that there are truly no longer any high-level dealers to grab.
(3) the incarcerated form a ready labor pool that - again - gets about 12-25 cents an hour to make a wide variety of products that allow American "manufacturers" to compete with Chinese sweatshops without having to pay for containers from Shenzen.
The opioid crisis is creating an opportunity for America to codify indentured servitude.