Answer:
The War (their husbands and sons were away as soldiers and as such there was no one to provide)
The Great Depression (The country economy was failing and EVERYONE needed to find a job)
Cost of Life (It was more expensive to buy/rent property and raise children, so everyone needed to chip in to stay afloat)
- P.S. I'm not exactly sure how many reasons and explanations you need, but in any case you can elaborate on these and expand on other ideas :)