Probably a lot of factors, but I'd say two are key:
1) Materialism and the wealth gap - Over the last couple decades the gap between the wealthy and poor has widened substantially, with a shrinking middle class. That combined with an increasing need to have everything, has caused most families of below wealthy means to resort to taking on multiple jobs, has caused an explosion of dual income households and often a resulting general neglect of kids, and also an exponential increase in debt. Higher stress and lower familial connections lead to a depressing life.
2) Diversity - We are happiest when we are among like-minded people. That doesn't mean we shouldn't be able to work with others, but after thinking my whole life that diversity was a great strength, I've recently come to the conclusion that it causes more problems than it's worth. As Canadians, we need to have a shared core value system in order to co-habitate peaceably. Unfortunately, our immigration process has very little to do with proper assimilation to Canadian life. After all, Canada's great strength is diversity, right? Assimilation is evil, right? The problem is that when people of widely varying core beliefs are forced to live in close proximity, day in and day out, it leads to increased hostility. The reason there's a big anti-immigration push in many countries around the world is because governments are pushing a principle (diversity is good and tolerant) that may not be practical in application, and are shutting down opposition by accusing them of being bigots.
