Technically people do owe taxes on revenue from illegal activity. You certainly could put a tax on something that's illegal, I just don't think it would bring in much revenue I'd you're still prosecuting people for that same thing you are taxing.
Here's line 8z on the schedule 1, as you can see and like I said, it's not specifically for income generated for illegal activity. It's for all other income, and since there's no box specifically for that kind of income, you'd list it under other income.
If there was a line specifically for illegal activity you'd put it there, but there isn't, so you put it in the catch-all 'other income'.
Furthermore, 8z is like form 8949 (sale/disposition of other assets) in that the description is blank for the filer to fill out, so one doesn't need to explicitly state that it's from illegal activity. If you're a fence and bought a bunch of stolen power tools and sold them at a profit you'd probably just want to put 'sale of refurbished power tools' rather than 'sale of unlawfully-acquired power tools'