Incentivizing events to be held at particular venues is standard.
It's pure economics - it seems that Alberta has the lowest personal taxes in all of Canada?
http://www.albertacanada.com/business/overview/low-personal-taxes.aspx
By providing an incentive, the local government will factor in the the cost benefits - hotel room tax, money spend while in the venue town - shops, food, restuarants, museums, galleries, transport etc etc - sure some events will bring in more dollars, others less. But, unless you've got events queuing up to use your venue, a venue full of JWs is probably better than an empty venue - both for the local government and the local businesses..
Remember there is also the benefit of indirect tax - the income tax etc you get from the people employed by the venue, hotels, local businesses and transport.
Sometimes I believe a local government will effectively sponsor a venue and related hotels and businesses - for example by guaranteeing that the venue will be used a set number of days-per-year.
On a smaller scale, it's like you personally organising an event at a local bar - the bar provides you with the room at either low or no cost as the bar expects to makes it's money from selling drinks and food to the people you are bringing in. The bar also does not expect your guests to buy their drinks from the bar next door!
