I think there's a lot more to it than that. The bikes are very different and much harder to ride in imperfect conditions, and promotions seem to be reluctant to run in front of rain affected crowds or pay expenses for rider's travel only for the meeting to be off anyway.
Don't get me wrong, Brtish speedway has got itself in this hole. But if you are going to have play offs then the season needs organising much better than it has been recently.