I'd argue that EAX wasn't really that sophisticated; it had a library of cheap DSP effects that was an improvement over nothing, but had no ability to transition from one to another, and didn't handle environments other than closed ones.
It turned out to be far more flexible and pragmatic to do it all in software, where developers weren't constrained by a single, indifferent hardware developer. (With bonus points for working everywhere, instead of requiring a single-source product). Creative was never interested in an API that would allow anybody's hardware to use it.
Insert OpenAL: Loki Software implemented an open and cross-platform API for 3D audio, with software fallback.For a while, OpenAL was one of the audio libraries of choice - Doom 3, BioShock, Unreal Tournament, Jedi Knight, Battlefield 2. Creative even deprecated EAX in favor of OpenAL.
But game makers were pragmatic and started doing the DSP in software, since it would work everywhere instead of being specific to Creative hardware.
I don't even know of modern software that supports anything like EAX in hardware anymore. (Well, other than Creative's Demos...)