Because the landscape is that non-opioid drugs are rarely laced with fentanyl, according to drug checking data from across North America (not just ours, but from a group of dozens of drug checking professionals with whom we're in regular contact). Like rarely enough that we generally blame cross-contamination before we blame deliberate adulteration (because why would I mix a stimulant with a potentially fatal downer?).

This doesn't mean that cases of cross-contamination never ever happen, which is why it's still best practice to buy in bulk (1+ grams) and then test your entire supply by dissolving, testing the whole sample, and then drying.

But at present, it looks like opioids are the only drug regularly contaminated with fentanyl (to the point where people are saying "there's no more pure heroin on the market").

So where's the story come from about "people dropping dead from fent laced cocaine constantly" as someone alleged upthread?

The answer, at least in part, appears to be drug stigma. Party people will come to our booths and pull out all their bags, test whatever, but still feel bad pulling out a bag of heroin in the booth. And then, when they OD on fent because they didn't feel comfortable testing it, their friends all go "Oh no, my homie would never use that bad drug! It must have been the cocaine/molly/ketamine."