A decrease in solidarity means people have fewer resources to turn to in time of crisis.
With a decrease in solidarity, a man either makes it on his own or fails on his own.
If a man is struggling to make it on his own, a child becomes an unwelcome hindrance. A child is an economic drain, and if a man has no other resources, a child might destroy his chances of success.
Thus it should come as no surprise that programs to provide economic aid to poor soon-to-be-parents would decrease abortion rates to some extent.