While I happen to think it's a really cool feature, I'll throw out a few thoughts:
1. The maintenance difficulty is likely the main issue. In addition to what Huck said about the lob wedges, I'd also add in other minor issues probably like drainage, washout, mowing annoyances, etc. You're also reducing the effective size of the green so there's more concentrated footprints. Probably one of the reasons most courses have larger greens than they used to as well.
2. I saw where, I think it was Justin Rose, missed on the complete opposite side of the bunker from the Sunday flag. While the announcers were quick to point out (and Justin ultimately wound up taking that route) the slope of the green allowing for the option of putting and still getting it within 8 feet, I would wager that most amateurs wouldn't have the first clue to look at that. As a result, it would be dismissed as gimmicky, when I think subtle genius is a more apt phrase.
3. Relating to that, and playing devil's advocate, isn't golf hard enough without putting a bunker in the middle of a green? Don't all golf teachers preach to simply aim at the center of the green as a way to reduce the scores? How frustrated would you be as a weekend warrior to absolutely smoke a 5-iron right at the dead middle of the green only to have it go in a bunker? Again, I'm playing devil's advocate because I happen to like the enhanced focus required on such a hole and the fact that "rub of the green" (basically) can leave you with a poor lie after a well struck shot.
CJ