These units, identical in capacity to normal buckets, cost between 20 and 100 times as much.
I imagine that they are popular because of their cavernous size. You should be able to fit a bottle of skin lotion, 2 extra sweaters, 5 pounds of makeup, and a small dog in one. With room left over.
This is one fashion trend I am fully behind. I hope someday buckets are even trendier!
For a gorgeous example of a bucket bag, look at this Ceyue bag. This is not just any bucket bag, it has a gorgeous pink motif and gold hardware, for an affordable price.
Update: I found yet more photographic evidence that buckets are now fashionable.