Many players prefer more realistic game-play and didn't want to be forced to have occults by them being slipped into expansions for other things. Aliens managed to fit in get to work because of the science career but even that got some criticism.
Personally, I'm all for occult. There was a survey recently by Sim guru Grant about a possible occult Game-pack. Witches came out on top, followed by Mermaids. So there's that to look forward to.
He also mentioned that they didn't intend to improve on plantsims.