There are other walking public courses in LA. Like Rancho Park.
In addition to the courses mentioned, LA County has 19 courses or so- a few of which are 9 holes- but essentially all of them are walkable. And not just theoretically walkable, but comfortably and consistently so. Likewise the Long Beach tracks (Big Rec, Skylinks, EL Do) are all comfortable walks.
OC has the Miles Square courses, Costa Mesa courses, the Navy courses and then the little guys like the Wick, Meadowlark, Dad Miller, Fullerton. Tustin Ranch is also quite walkable.
Granted, they are crowded (and/or expensive.) But its tough to blame architects for that problem. As it happens, the LA Area has a lot of people and many of them seem to want to play golf.
More generally, looking at the list of recent courses (and adding a few that aren't on there like Westridge, Black Gold, Coyote Hills) it seems to me a bigger issue is that it is going to be very difficult to find a chunk of land in LA/OC that can accommodate a comfortable walking course. However they were routed, Pelican Hills was going to be a tough walk giving the terrain involved. Some of the others on that list suffer from similar geographic constraints.
It would seem that the biggest issue is that it is very hard to get the acreage you need to build a new course in the LA/OC area. To the extent that you can get it, the odds are that it will either be hillside (and thus tough to walk) or the acreage will be part of a much larger development (fostering the necessity lengthy transitions) or feature some other challenges (flood control, power lines, environmentally sensitive areas, freeways) that will also make it hard to design a compact lay out.
To be sure, worrying about whether or not a course is walkable is a very recent consideration for me, and not one that personally interests me all that much, so I could be off on this. And I'm sure some of the recent courses could have been made much more walker-friendly. That said, I think suggesting that the lack of recently built walkable courses in LA/OC is simply a design issue misses some of the complexities of why that may be.
And besides, there is always the Goose!