It's very difficult to get accurate data, but I'll hazard a couple of comments:
These days, the use of enemas to relieve constipation is largely obsolete. Due to a lot of marketing money, an enema has come to mean either a small, single use, bottle of solution or a smaller applicator. These are easy to hide, easy to use even in a public toilet, and usually makes someone poo quickly. Not comfortably, but they do work. They are also single use, so next time you have to buy a new one. Bags and cans are sold one time and wok fine for decades.
In the UK they were also kept behind the counter, and laxatives too, as I remember. I suspect because needing help to poo is somehow considered ‘not nice’. Years ago, in the US, birth control stuff was kept behind the counter., I was once asked by a druggist if I was married when tying to buy condoms or foam, many yeas ago.
Now, enemas have become much more common, although it's often called ‘anal douching’… obviously because anal sex has come far more out into the open.
I would guess that in countries where anal is not acceptable enema are pretty rafe.