I thought the only purpose of a patch was to fix broken parts of the game?
Nope, they can add stuff as well, and already have.
As far as why it was left out - people have explained it rather well already, this is all stuff that happened after the game's completion and release. Without any deadlines to worry about, all studios in house (not just Bethesda, but
all the studios under ZeniMax) got together for a week, and without having to actually develop content, were able to just add in whatever features they wanted. That's where all of this stuff comes from. Some of it has already been added, and I'm sure we'll see much more of it in the future as well.