The movie is a huge bomb for a number of reasons. 1 is because the Skrek franchise has been a cashcow for Dreamwokrs since 2001. Besides the 1st Skrek, Skrek 2 and 3 each made well over $700 million dollars. To drop from that to not even that much over $300 million so far is not a good look. Especially when you consider the film had the highest animated film wide release to date with well over 4,000 screens, 3-D ticket prices as well as the budget which was over $160 million and marketing.
2nd, Dreamworks has only made about $140+ million dollars off the movie so far which isn't alot especially for such a huge franchise as Shrek. Profits have to be divided remember. The budget, marketing, movie theater percentage, money paid out to shareholders etc. Dreamwokrs was betting alot on this movie which is why the stock as well as the financial outlook has gone down because in all aspects this film is a flop. If Harry Potter and the Deathly Hollows makes only $350 million a month after release when it's such a huge franchise with a budget well over $200 million, then that film would be considered a flop as well.
The film staying at the top of the box office for 2 or 3 weeks means nothing when the competition is sub par or not huge box office draws in the 1st place. What competition did Shrek have? The money the film made in it's 1st month is still less or just slightly more then what the last 2 films made in their 1st week in release. To go from over $100 million with cheaper tickets and no gimmiks like 3D with the last 2 to making only $70 million 1st week with all the elements that weren't there when Shrek 2 and 3 were huge hits is a huge slap in the face to Dreamworks. The movie business is exactly that a business and Shrek 4 has not done the type of business Dreamworks expected or the type of business that was expected from such a once high profile franchise like Shrek.