A better question is: Why can't I have it in a VST? ReWire is a PITA.
To be fair this might just be linux on this machine, it's an old mac and I had only run software synths on it in OS X before (which were playable, but I know xnu has been tweaked with low latency audio in mind), maybe I need one of those special linux kernels to get low latency on this old thing.