Changes in fertility probably resulted from a decline in infant mortality (in the past, wanting two to four children who lived to adulthood, required ten or more pregnancies). Antibiotics and improved surgical techniques (e.g. ability to do a ceasarian other than to rescue a baby whose mother had just died) meant humanity can survive without women having to spend their entire adult lives producing children. Combined with a collapse in maternal morality (formerly the leading cause of death for adult women), this lead to a greater number of women getting jobs and a willingness to invest in women’s education (since they were now surviving childbearing). This has been true in all countries, though is more obvious in the ones that industrialized first since it takes a few generations for birth rates to fall. It is hard to say if it will be good or bad in the long run, since more educated women (and education for women became cost effective when their survival became the norm) arguably make better mothers.
The frum community has hardly rejected the overall trend. In the period before industrialization most women received minimal education. They could read books such as “Tzena u-reina” but that’s about it. The average Bais Yaakov girl is on a vastly higher level than the average frum girl of 250 years ago (not to mention she is likely to survive childhood, childbearing and live to old age, something was exceptional back then). Also note that 250 years ago very few frum women were unemployed since they usually supervised large households, helped run business or if they were poor, worked as servants (remember most housework done today with appliances was previously done by servants, and anyone middle class probably had servants, and for obvious reason Jews were preferable as live-in servants). Unless you favor banning antibiotics, anesthesia and electric appliances, there is no going back to the “good old days”.