I could offer a handful of reasons, but the top one would be that they don't want to maintain it. Probably, the developers had Rifts, they wanted to play around with the tech, and they were gambling a bit on the development of the Rift during the development of the game engine (the right time to get involved, if you want to be first-to-market, so a smart move).
However, very few people own Rifts, and so if they left this in, Rift users finding bugs and incompletely-tested code would need to be supported (otherwise, PR nightmare).
When people use the "hack," they have the company has the option of saying, "That's not officially supported, you had to change things in order to do it." So, when there are bugs and things that don't work very well, the company has its hands clean, the enthusiasts still get to fool around with their early-adopter toy, and the company looks better in the long run.