The Borden Dairy Company was founded in the 1857 by Gail Borden Jr. (hence the company name), it later came to Canada just before the 1900's. Furthermore, the legendary 'Elsie the Cow' was created in 1936 to symbolize "the perfect dairy product".
The year listed on the front cover of the pamphlet is 1942, this is right in the middle of the second world war, therefore there may be some connection. During the war, families had less money, and the women had less time to spend cooking, because they were working in the factories. Condensed milk was created to last longer on the shelves and in storage. It has more sugar so that it can last longer on the shelves, and also is a lot easier for baking or making cream sauces. It is also not expensive when compared to regular milk.
During the second world war, processed food became more and more popular because they were less expensive, quick and easy. This pamphlet states that the condensed milk they use in each recipe is “soooo good for you” or “good for babies too” and this just goes to show how old it is. I don’t know very many moms feeding their baby sweetened condensed milk.