Anyone with their own "ueito" in Japan for this?
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Because it is considered a form of gambling. You are paying a fixed price for an amount returned with an house determined random probability that you will profit from it with no guarantee. This is effectively how a casino operates.
This was very popular in with the European sail traders (especially the Dutch) when unloading inventory at the end of a season. Eventually, it made its way to Japan.
That is not the reason. Go online and do a search for something like, "mystery bag", or "mystery box" sale. There are plenty of retailers that do such things in the United States. There is nothing wrong with selling a person a mystery container. Look at the storage places that sell, mystery abandoned storage containers, with people buying them in hopes of some expensive find. We have TV shows devoted to that.
The reasons we don't do it in the United States is likely for the reason somebody else stated. Culture. This is part of the Japanese culture, like shooting off Fireworks on July 4 is for us. Further, Japan is a much smaller market than the United States. As a practical matter it might be harder to implement here.