You can read the entire article at GateWorld.
Basically it comes down to numbers - and Engler even provides a chart (right).
There have been arguments that the the show's hiatus was responsible, that SYFY wanted wrestling and that SYFY didn't even like SGU.
Engler addresses all these issues and more.
Here are some:
The hiatus killed SGU:
As you can see from the ratings above, the biggest drop in viewers came before the hiatus, not after. In fact, SGU actually grew around 10% after the hiatus between season 1.0 and 1.5 in its first two episodes back.
If you’d left it on Friday nights, it would have done well:
When left on Friday nights SGU lost 1/3 of its audience and dropped to consistently unsustainable ratings levels. The only hope of keeping it was to move it to another night where new viewers could find it.
You canceled SGU in order to make wrestling:
We would have happily kept making SGU regardless of anything else on our schedule if the ratings were sustainable. We don’t discontinue successful shows to make room for other shows … no network does because no network has a full roster of successful series. SGU was judged solely on its own ratings.
You don’t like Stargate:
We love Stargate. Combined we’ve made 12 seasons of 3 separate series and helped support two SG-1 films. It’s been an amazing ride and we’re incredibly proud of the cast and crew of all the shows, and thankful to all the viewers who watched.