Mainly because of a shortage of income.
I talked about municipal taxation, for instance. Municipal taxes have been increasing significantly. There are cities in Quebec where they have increased by 9%. Those who are only receiving benefits from the Régime de rentes du Québec, or the CPP and OAS, only have these small amounts indexed. Municipal taxes often increase much more quickly than that, so their income is getting smaller from year to year.
It's the same for renters. They live in a building, which is also subject to a municipal tax, and an increase in this tax frequently affects the rent. If OAS payments don't rise sufficiently, they have to move or sell their house.