I think drug addicts tend to hit bottom younger and faster than alcoholics. You can be a functioning alcoholic for decades. I certainly was. I haven't seen anyone be a functioning drug addict for decades.
I also haven't been to an NA meeting that has many members with more than a few years clean. I think it's a great idea for addicts to come to AA meetings and hear from many people with decades of sobriety through practicing the Steps, if that's what they want to do.
I didn't know I was a drug addict until I after I discovered I was an alcoholic, which didn't happen until I found myself in AA. Who is to say that people won't need to hear what they need to hear, regardless of which fellowship they hear it in?