Why? Now that it is more difficult to evict tenants and it takes longer to get them out (all the while the landlord is losing rent), landlords are becoming a lot more 'picky' about accepting tenants in the first place. With a vacancy factor of less than 1% for condos (apartments are over 3%), the market is in their favour. Landlords are not obliged to give a reason for a decline - just not acceptable. If a landlord thinks a tenant may prove difficult, then they won't rent to them in the first place.
Also rent deposits of more than the last month are illegal. Tenants with bad credit or who have no assets or a job in Canada often gave extra months rent. Now landlords are either refusing these tenants or are asking for a rental guarantor. Good luck in finding someone who wants to give a guaranty. If you are a parent with university students who want to live off campus, be prepared to act as a Guarantor!!