In that state, a significant amount of arrests, convictions and revenue from fines came from marijuana charges. Each conviction came with hundreds to thousands in fines.
Not only that, each conviction created busywork for probation officers, as low level offenders were given the option to have their record cleaned of their conviction if they went on probation programs where they are drug tested regularly. The probation program came with more fines/fees, as well. It also opened opportunities to keep people in the system, because violation of probation has its own penalties. Kids' parents have the incentive to push kids through this program and to pay for it, too.
There are those reasons, and then there's the simple fact that cops know they will have less to do if they can't arrest people for pot, which might be bad for job security. Losing "I smell marijuana" as a method for establishing probable cause was a big deal, as well.
Arresting you improves their metrics and helps justify the labor hours that ultimately pay their bills. Also it's used as a pretext to steal billions of dollars via civil asset forfeiture much of it in less than $1000 increments.
See literal highway robbers stealing $500 from citizens via lawsuits like state vs 535 dollars and 75 cents where criminal intent is inferred but no proof is given.
But why though? Hatred? Inertia? Culture? Do they get paid per scalp? Do they love their drug dogs that much?
The lack of arguments against pot-smoking notwithstanding, what is it that backs this? Because so much of this seems completely arbitrary.