With sim work there is the cost of the sim and the cost of the person driving it.
If your doing none approved sessions the costs are reduced because anyone can run the sim.
And as most of the sim cost is fixed costs with approvals and maint any thing which increases your cash flow outside when approved courses are run is money in the pocket. If its sitting there doing nothing you get nothing if its running with a bloke getting payed 20 quid an hour and you only have to pay for the leccy its a pretty good profit margin.