Simple, first there were a lot of them made.
Second, lots of people found out that tiny guns are unpleasant to shoot.
Third, others have realized that bigger guns are better and, with a good carry rig, can be easily carried.
So the supply of these guns is huge. Many of us have them as back-up pistols and use them as a BUG. Some folks use them as primary carry pistols. And people who bought them thinking that a small gun would be easy to shoot have woken up after shooting them and decided to sell them to buy a larger/heavier gun with a real grip and similar recoil but easier to handle and firing a bigger/heavier bullet.
The are singularly ugly as far as revolvers go. This is my idea of a nice, compact revolver:
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