Shipments do not always represent sales expectations. Shipments represent retail expectations. Which is to say, if a game has high sell-through, this is good for retailers because it means they have correctly judged how much of a game to order, and they are unlikely to be stuck with a ton of unsold stock in months to come.
A publisher cannot decide entirely on their own to ship exactly what they want to sell into the market. Retailers will not pay for stock they don't want. There are various methods that big publishers can force a higher shipment if it is a major franchise, and they have special conditions for orders being placed. In the case of lower selling titles, a small initial shipment simply reflects a lack of retail demand via preorders and general consumer interest before the release of the game, thus it would be impossible for the publisher to ship much more than that.
When you develop a game, you might have expectations that the game needs to sell 200k for example, for it to be successful. This is a sales expectation. When the game is done, maybe no one wants it at all, and so you are only able to ship 80k at most into retail. If the game then sells 70% of that in the first week, it does not mean that the game is close to meeting sales expectations, merely that retailers were cautious on it and they are rewarded by not having overstock. If the game does not continue to sell, and eventually retailers only order another 20k, the game will still have sold 100k in total and missed the mark of the 200k expectation by half.
I hope that explains things.