So what the heck has changed in the last 20 years that this is somehow become "an issue"? That we should throw all that history and all that tradition out the window now? Its silly beyond the point of absurd.
I'm not sure it is limited to the past 20 years, but the answer is the general expansion of rights and the erosion of marriage as a cultural necessity.
Back in time when women couldn't work and were merely the property of their husband there was substantial social pressure for woman to get married to avoid being a burden on their fathers and brothers and for men to get married to have heirs. Once we recognized that women aren't merely property, the pressure to become married gradually eroded, to the point where no fault divorce and children out of wedlock have become acceptable behavior with virtually no stigma.
Once it became acceptable for people to remain unmarried and still satisfy their sexual urges, homosexuals started to realize that they can also satisfy their sexual urges and don't need to enter a traditional marriage with secret sex partners on the side. After homosexual relationships started to gain acceptance people and based upon the erosion of marriage as the only acceptable social form of lifestyle and child rearing, people started realizing that a government stamp of approval for only traditional marriage is silly.
Another factor beyond just social progression is social services. If a woman in the past slept around and got pregnant, it placed a burden on the family. Thus, you had fathers taking more care to insure it didn't happen and/or to force a marriage when it did, and mothers teaching public shame to discourage women from giving it up for free. When the government starts paying for out-of-wedlock babies and forcing child support regardless of marriage, it takes the burden off the families and makes marriage less important as a survival tool.
Further, non-wealthy people and people without a pension (or their husband's pension) used to depend upon their children to survive retirement. However, with greater understanding of financial planning, tax laws and incentives to promote retirement plans, and social security, people are better able to provide for oneself in retirement, without the need for children.