When machines were cash only you could theoretically avoid taxes on some of the income, something that might have offset some of the hassles. With credit cards and electronic payment that’s not really possible.
It's not a fast, discreet, or easy process.
They are big and bulky and heavy and all that work for, what, $80? Junkies aren’t usually that coordinated to pull this off.
$80 sitting easy is great for a junkie. But requiring multiple steps and special equipment may as well be a voyage to the moon.
For proper criminals who can plan and procure equipment, $80 probably isn’t enticing.
And that's assuming your vending machine isn't using some standard key you can just outright buy on ebay.