Historically it's been because one drug (alcohol) is legal and most other drugs used for recreational purposes are illegal.
However it took a long while before alcohol addiction got respect.
There are also those who scoff at the idea of attaching addict and disease to everything. Some people for example hate the term "sex addict". They refuse to acknowledge it's even possible to be one.
Imagine a wife busts her husband having several affairs or seeing prostitutes and strippers behind her back. He along with his doctor inform her that he is a "sex addict". She believes it's an "excuse"!
Odds are more wives will support their alcoholic husband by going to meetings and learning about that disease than there are wives who would empathize with husbands who have a sex addiction disease. There's no "empathy" for coping with certain addictions.
Addiction is an impulse to pursue having something regardless of the personal cost. Today "hoarders" are considered addicts, gamblers, high levels of sexual promiscuity, and some people are diagnosed as "food addicts". Take away whatever the addict enjoys or "needs" without help and you'll see them go to great lengths to get their fix.