Because its an overpriced piece of crap. There are much better alternatives that are cheaper or barely higher than it on Creative's Sound Blaster Series.
The ZxR is literally ~$20 more, and the Zx is around $70 less, both offering a solid headphone amp, dedicated front/sub/rear connections, and a dedicated headphone out. With the ZxR having much more options in terms of expandability.
Oh, and from experience, the sound quality from the Zx/ZxR both sound infinitely better than the Phoebus.
The Phoebus is just flat out garbage.