Well because I have a three year old XFX 650W PSU and I like to eventually replace it, plus it's made by Seasonic whom I trust more than anything when it comes to PSUs
My first system build used an Antec PSU, now I don't have any because there have been good competitors. The new Edge line looks promising, well-reviewed, so I'd like to try it out.
The reason I would want to run an Antec specialized Power Supply is the fact that my current power supply is extremely old. I'm surprised it is still able to power my system.