It had a production budget of $7,000,000, but that doesn't include the cost of manufacturing or advertising. And the gross revenue doesn't indicate the cut that goes to retailers where the DVDs were sold, which could be quite substantial, especially at the inflated prices the movie was sold early in its release.
And the best indicator that these didn't blow MGM's socks off: additional DVD movies are dead in the water, despite the fact that scripts for at least two of them are already completed.
There's also the fact MGM was going bankrupt. That's not to say that the performance of the DVD sales wasn't underwhelming, but I don't think it's an accurate picture of the whole story either.
When you are bankrupt and restructuring, you focus on things that are profitable and slash everything that's not. That there are no further SG movies on the horizon should tell you how it balanced out from MGM's end. If they made decent money, they would be an important part of a restructuring package. While the Stargate franchise may be worth something to MGM, it is evidently not worth enough for them to invest money into it right now.
The release of Continuum was followed almost immediately by the recession and the ass falling out of the DVD market. A relatively safe yet small earner got a whole lot more risky over night, plus compared to The Hobbit and Bond a Stargate DVD movie is small potatoes.