and the population of Los Angeles is well over 12 million.
on the other hand, Lambeau Field seats about 80,000 and the population of Green Bay is only about 100,000.
First preseason game:
But - trying not to sound like a snob here - California does offer a lot of options. There's a reason so many people moved here: it's a very active state, especially early in the morning when there's tons of people out riding bikes, jogging, walking, etc. Visitors always seem to remark how busy it is early.
The thought of driving to downtown LA to watch the Rams when it's really nice outside just doesn't compute with most. That's why LA (and "SF" now that they're down in Santa Clara) will only support a winner. Not because they're band wagon fans, but rather, there's so many other things to do.
Green Bay, like SF used to be, has weather/culture more suited for the social aspects of football. When the 9ers played at Candlestick, it was much cooler and felt much more like fall.
Throw in the political aspects, and my own theory (the NFL has destroyed the game through constant commercial/penalty review interruption), and we see the result. However, perhaps the most interesting trend is the growing active FU boycott. That is, agnostics like me can even feel the impulse to jump on board to make our general malaise & boredom wit the game more of a political statement just for the hell of it.