The difference in cost, between a kilo of pure heroin, and a kilo of pure cocaine, is staggering. In fact, it's no comparison at all.

Also, the difference in both strength, and the amount of times each of those two drugs can be "diluted" and "stepped on," as the street vernacular goes, is also staggering.

You could take a "pure" one ounce bag of heroin, "step on it" say 10 times, turn that 1 ounce into 10 ounces, and the heroin would still be amazingly powerful. Strong enough, so that a single doze could still overdose you, and kill you.

But if you took an equal amount of pure cocaine, a one ounce bag, and "stepped on it" 10 times, turning it into 10 ounces? Then you might as well throw it all in the garbage pail, because at that point all you'd have is garbage.
-
The ability for the main heroin importers and wholesalers to convert a single kilo into ten or twenty kilos (off that single kilo), thereby making a 1000%, or 2000%, profit overnight is why the heroin trade was always king. Add to that it's potential to create legions of addicts all craving the drug, and you've got yourself a built-in, never ending, supply of customers.

Cocaine, is a different animal. Both in its addictive properties, and the ability of suppliers to "cut it." Most top level cocaine importers-dealers never cut their product. They feared diluting its potency.
-

Today, with Fentanyl, its a different story altogether. But back in the day, that deadly substance wasn't even a thing and hadn't been invented yet.