Mystery boxes- why do they suck so often?

Because, by nature, they are made up of stuff you probably wouldn't buy if you knew what was in the box. That's why it's called "MYSTERY box" instead of "Random DVDs you don't want" box.

If they could sell the product to you and you would buy it knowing what it was, they probably would.

I haven't ever bought a "mystery box" but I have added a couple "mystery items" onto my order on occasion. For under $5 I don't expect much and I didn't get much. One time they gave me a couple of plastic gizmos that snapped onto a pop can and gave it a neck and cap like a water bottle. Useless to me since I tend to chug pop, but my kids liked them until they broke after about a year.

IME / IMHO -

When a company views a "mystery box" or "grab bag" or "bag of crap", etc., as a way to liquidate cheap shit no one wants at a profit, they generally suck. There are precious few exceptions. Google is your friend - just make sure you're reading actual customer comments.

When the company views the offering of said boxes as a loss leader to keep / attract traffic (members), they're usually great - but they're generally greatly limited in quantity and sell out very quickly.

Meh gets it right. woot! USED to get it right. Before eBay killed the "mystery box" sales, there were a couple of sellers (both toy sellers) that got it right every time ($10 or $15 delivered got you $50-100 retail value in NIB sealed toys / games / plush).

We've been burned by more than we've enjoyed - so now we're quite picky about where we look for them to be offered.

Usually, by the time you hear about a worthwhile "Mystery Box" it has already jumped the shark. The reason is, the demand it puts on the vendor can no longer be sustained. The expected level exceeds reality. This happened with BOC, Allure Boxes, Mystery Boxes from various vendors, etc.
While the concept works - get rid of excess inventory, one-offs, demos, returns, etc. It just isn't a sustainable business model for long.

Ooo! Ooo! I actually know the answer! No, really! It comes down to the difference between a product and a promotion.

A fuku (or pre-2013 BOC) isn't really a product. They're available for a limited time and in limited quantities, and when you buy one, you've essentially won a little mini-contest. What you get is going to be worth several times what you paid, and unless your expectations are totally nuts, you'll be happy. Why would they send stuff at a loss? To generate excitement, intestest, and buzz. People who get good mystery packages tend to post about it, do unboxing videos, and generally tell their friends. And unlike a traditional sweepstakes with a car or trip prize, there can be a comparitively large number of people who win. Happy customers, lots of good buzz, more site visitors, everybody wins.

So why do other-site mystery packages tend to suck? They try to make them products, and to have a built-in profit margin. It costs more to ship a package than most people think, plus there's fulfillment costs and of course the items themselves, so making any kind of profit is very difficult. Vendors will tend to skimp the only place they really can, which is the items. If you buy a $20 box you might get 3-5 items that can be bought wholesale for less than $1 each in bulk. You're very likely to be disappointed, and the site gets buzz of the wrong kind, angry/disappointed unboxing videos, negative reviews, and even some BBB complaints and chargebacks. Not good.

The best thing to do is just not buy mystery packages other than the Fuku, or potentially the BOC if Woot ever cleans up its act.

[Note: none of this applies to monthly subscription boxes like Loot Crate, those are a whole different animal with a different business model.]