Localiser Green -
Monarch have nothing against time share owners, it's just that Friday flights are more popular and so Monarch can sell them at a higher price. It's a less extreme version of the load management strategy that most airlines, particularly the lo-co's, use these days.
If you can travel on Thursday the prices might well be cheaper.
In addition, a TFS rotation is a difficult one as it is about twice as long as the average low-cost rotation and consequently difficult to fit in to the program. However, if demand warrants it I am sure you will see an increase in the service.