Typical answer would be limited development time.
If you had:
1) Devs spend time building a feature and balancing it you don't want
2) Since the above requires scripting knowledge, it they could have added in more patrols, more random encounters perhaps even a virtibird crash landing that was talked about in another thread.
If you had no interest in a hardcoe mode, which option would you choose given those options? Lets face it, creating and *balancing* a survival mechanic takes some time. By no means, take this as an attack, I actually do want the mode. Just without the pointless eating/drinking/sleeping mechanics that nv used.
On the other hand, I think this might not even be an issue for the most part. I was listening to an interview with Tod Howard, and he was talking about balancing the economy and getting rid of cash exploits. Ammo that has 0 weight and a cash value.. would be one hell of an exploit in theory. And its not to far of a stretch for them to have added in the medical bits from nv hard core mode as normal game play. Or making stims heal over time in the base game. Otherwise it was just a god-mode switch.
That being said, I can see them re-enabling the instant healing stims in say the easy difficulty mode. *that* would be a simple switch, and would make sense for folks that have a difficult time with the normal difficulty.
*shrugs* Only 1 month 3 weeks 21 hours until we find out for sure!