Jim,
There's no doubt that more TLC is needed, given the immediate surrounds of that bunker, but, if Riviera hand mows and rakes their greens and bunkers, I wouldn't imagine that the incremental cost would be prohibitive.
And, that bunker has become an icon of sorts, sort of unique to Riviera, so I'd imagine that they'd want to preserve that feature irrespective of the cost.
I can't imagine the cost to maintain it is that much different from the Road Hole or Eden bunkers, both of which can't be mechanically raked, and have the same difficulty in getting sand into them.
I'm trying to remember how deep/shallow that bunker is.
I'd imagine, without the proper drainage, that that bunker could never come into existance.