Because clubs have found that stakes levels have virtually no impact on field sizes and punting within certain ranges. Increasing stakes by $2,000 a race would cost Westport $40,000+ over the two days with no impact on field sizes and turnover.
A classic example is today's Pukekohe gallops. On a soft track and with reasonable weather they have increased stakes by $3,000 a race, a 25% increase, $24,000 over the 8 races. They have field sizes of 10,8,5,5,7,7,4,8. Almost as bad as the Auckland trots. Must be an Auckland thing.
There is no incentiove for clubs to contribute any of their own money these days. They have all had the stuffing and any sense of enthusiasm kicked out of them. The only Southern club that makes much of an effort is Riverton who run for $15,000 on New Years day. The Invercargill gallops put an extra $20,000 into their Guineas race, but I doubt it attracted one extra horse.