Other for a couple of reasons:
Playing:
Few DMs I have played with want to deal psionics, because they feel they have enough to deal with already or don’t want to buy the book. For those DM that did sound interested:
The first DM was doing a high-level one shot slugfest and didn’t even read the material. He trusted me to run my psiwarrior on my own.
The second DM is running a RPGA Living Arcanis game, which allows psionics. However, the rules for psi in L.A. is pretty strict, it is only PsiHB with the Slayer PrC being a restricted and currently unkown class. And after seeing that the PrC’s are not modified to the “+1 existing class” advancement that Blood and Tomb and WotC website Psionic PrCs are, it doesn’t seem that cost efficient to aim for a PrC. I can understand where they are coming from though. (Any L.A. players want to sign a petition?). With the foreknowledge of knowing what is available, playing a psionic PC is L.A. seems bland compared to the 10 or so PrCs one can get from the class books for non-psionic careers.
I have one DM who is saying “When I do run, let me read what it is you want to run from the PsiHB, WotC website and ITCK and I’ll think about it.” But he’s not ready to run yet and he’s only the third DM who has seemed open to psionics since the PsiHB has been out.
GMing:
I run more d20 stuff, Deadlands, Farscape and Spycraft so there hasn't been a chance to use the PsiHB yet. I just started a Space Fantasy homebrew and plan to use psionic powers instead of spells for my own variant of Dragonstar’s Spellware system. In the case of using something for generic powers, psionics may fit better once you house rule away the audio, visual, etc special effects (“Look! I am using a power! Hit me! Hit me!”). The powers as described are less flashy and their lack of scaling makes them less of a worry.