In one state where legalization was approved by public mandate, the legislation that passed made it so anyone under the age of 21 could only receive a warning for possession, and no charges or arrests.
This is important because any drug arrests, charges or convictions make individuals ineligible for federal student loans or assistance for college, meaning the kids who do get arrested might have their plans to better their lives ruined by a cop who doesn't like the smell of marijuana.
Police unions spent months and millions of dollars lobbying the state government so that they could still arrest and charge kids for pot possession.
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.
