Normal
It's not so much a question of running out of good tables as it is a question of running out of tables that would sell well. Remember, it's not enough for a table to be good...FarSight also has to (at least) make enough from that table to cover the cost of developing it for TPA. The older tables are especially prone to this because while an enthusiast may appreciate their gameplay, they may not be "flashy" enough to attract the casual player.