There may be perhaps 35 million monarchs surviving this winter, which sounds like a huge number, but you have to remember how delicate and small they are, and how those 35 million monarchs spread out across thousands of miles in the summer in a landscape with little habitat left for them. There used to be a billion or more monarchs that migrated north each year, so now scientists are worried that at some point, they will stop migrating north, especially if their numbers keep declining.
Monarchs have been in such sharp decline due to habitat loss in Mexico and the U.S. and Canada (from both conversion of prairies and natural land to farms and developments, and conversion of traditional corn and soybean fields where their milkweed host plant grew to herbicide-resistant crops with no milkweed) and from extreme weather, such as freezing events, drought, and timing of warm-up in the spring. Even if we happen to get some favorable weather years, we really need to plant native milkweeds in as many places as we can and avoid treating it like an unwanted "weed,", and also restore habitat throughout monarch's migratory routes, and hope that they can reverse their trend so future generations of Canadians, Americans and Mexicans can witness this
The New York Times article:
A Washington Post article which has some slightly different content and people interviewed: