I believe it also has to do with the "target audience" of each drug,if you get what i mean.
Coke and Meth are often viewed are recreational drugs where one can do every now and then,is popular among young ages,teenagers,college students and stuff and are accepted in more "normal" circles,whereas heroin is always viewed(falsely imo) as the lowlife drug for second class citizens,bums,deadbeat junkies etc.
People can go on days of stim binging themselves but god forbid if they find out youre doing H,you are immediately labeled as a sick unreliable junkie by those same ppl.Its a cultural thing i guess,theres that prejudice against heroin and thats where the needle comes in i think,as ppl have the theory that once a guy uses heroin hell go like mad or something,throw immediately his life and everything out of the window and start shooting into his dick cause he gives no shit.
Horrible stereotype imo,im around my 7nth year of active H addiction and never IVed once,even though i had plenty of chances and sometimes it was my only way of getting fixed but still refused and waited till i get some powder to snort/smoke.
Truth is that wheres smoke theres fire,meaning that the stereotype is somewhat true as alot of H users will quickly or eventually turn to the needle(for a variety of reasons) but thats only one side of the coin.
Plus,beside IV heroin being supposedly "great" and stuff,IV coke is way more intense and habit forming,most IV users agree on that,and its certainly more dangerous as well.