That is the point. By making it over-the-counter, the pharmacists and techs would not be involved. You would just look on the shelf under "suicide". ;>)
Excuse me Sir, "Which one works best"? "Fastest?" "Is this one the most painless?" Then you've got the 16 year old kid forced to sell it by checking them out.
Can I see your ID? "Friends" buying for minors?
Then there's the probability of those who'd use it to off people who are unaware, something like abort them both because a pregnancy is bad timing. She was despondent, because of the pregnancy.