The subject of the article obviously was at least semi-content living in SF, as he definitely had the means to depart if he wanted to do so. My list is meant more as a general reply to "why wouldn't someone want to live in one of those places?" It may just be my background of living in several different places, but personally I have a difficult time grasping why people assume that LA, SF, NY, or Chicago are the only reasonable places to live.
And, places do not have to be dirty, crowded, or high-traffic just because a lot of people want to live there. If things are designed reasonably and the populous behaves reasonably, traffic should continue to flow, there should be adequate personal space, and thoroughfares and public places should be clean and satisfactory.
No man is an island. The people you surround yourself with matter.
I agree that dependent on the level of immersion necessary, serious improv practitioners may find places that aren't the cities you listed restrictive, but there are well-attended improv troupes in other areas.
(The last actually fits in (b), but for a different attitude than the others.)
And the person in question is at least of the generation, and arguably of the attitude referred to in those other than the last, so its a pretty unconvincing list of why you'd think that person wouldn't want to live there.