Because he'd know exactly where he will be riding on what day week in week out. Iversen has rode here for years so doubt its about money for him, more about what he thinks is best for him to become world champion. Coventry Bees for example had 5 meetings in 12 days then zero meetings in 12 or so days, riders dont want that imbalance. I really don't think riders would drop Poland even if they paid less as its one meeting a week.