"My question is why weren't Canadian Grey wolves her before?"
"Canadian Grey" is a misnomer and used colloquially, sometimes causing a bit of confusion. The Gray Wolf (Canis Lupis) was in fact spread throughout the US before it's extirpation via subspecies of the Gray Wolf, including California. The actual subspecies inhabiting California isn't exact, but there were 'probably' at least 3 subspecies that roamed the state.
"Rocky Mountain timber wolves were predominant in ID, MT, WY, etc. they introduced Canadian Grey wolves. Why weren't they already in the US?"
Again, "Rocky Mountain timber wolf" is a misnomer. There are at least a couple subspecies that are 'commonly' referenced as "Timber Wolf". Perhaps you are referencing the Northern Rocky Mountain Wolf (Canis lupus irremotus), which roamed--as it's name states--areas of the northern rocky mountains, including California, along with other subspecies. And yes, they were in California before. The subspecies that was introduced into the YNP was the Mackenzie Valley Wolf (Canis lupus occidentalis), which is also referenced as 'timber wolf'.
The reason for introducing this particular subspecies is interesting, you might want to search it for future reference, but it is what it is.
I would prefer the wolf not repopulate California (and other states), but there is nothing to be done to stop it. As one of the previous posters stated, the only way to keep predators in check is for the state to manage that population, with hunting being the primary means of control. I sure don't see that happening in California either, given the political and population mind sets in general. As also mentioned in another post, with the cyclic roller coaster of un-managed predators, the predator/prey population dynamics would certainly ebb and flow, but wouldn't have the wolves eating themselves out of a food source.
Any way one looks at it, it's a pandora's box for hunters and our game animal populations, in one form or another.