Poaey bumpy greens he can't make every single 10 footer on
That's a good start, I think. He may have had more trouble reading those greens than most, too. The way the course sits down in the canyon, it's hard to notice the subtle fall toward the far end.
All the trees out there are certainly a factor -- less ability to make a brilliant recovery from a wayward drive.
And don't forget, the kikuyu fairways and roughs are just a different surface than anywhere else the pros play. For someone whose iron play and recovery play was as precise as Tiger, perhaps the different surface affected him in ways we wouldn't readily understand. I don't remember any of his flop-shot heroics coming at Riv.
Tiger was always head and shoulders above others when it came to plotting his way around the course and avoiding the things that must be avoided -- if there's something about Riviera he couldn't figure out, I don't know what it would be. But if it IS the grass around the greens that gave him fits, there's not much way to plan your way around that, anyway.