I think it’s the other way around. It has become so hard to start a family (focus on career, difficulty finding suitable partners, affordability of raising children…) that younger people are now doing it vicariously through their pets.
No. People aren't religious anymore and realized they don't need to make a kid to be a good person. We realized it's way, way not fun not to make a kid and have to take care of it.
For single women, it is their substitute for a husband and family. And sadly, it inhibits the achievement of both because dating a girl who always has to be home at 5pm to "let the dog out" of her 700 square foot hovel is annoying. Harder to travel too.