The treatment / rehab / injection / addict housing programs (and more) that are required when you decide that having people use drugs isn't something that they believe they will be punished for anymore and no longer exercise some measure of self-caution to avoid falling into. The near-hospital-like facilities and salaries of people you have to pay for to replace that self- or state-policing, and now have to clean up after those who have been given free license to use drugs, and get them back on some productive life track.

As GP was alluding to, all the things that require spending $ on, which people aren't apparently willing to spend after the symbol of voting for decriminalization. Which, if they're a mandatory part of decriminalization, but people never end up paying for, mean that decriminalization isn't actually a viable policy.