Implicit dowry system doesn't help - bridegroom's family is meant to stump up substantial funds in order to gain acceptance from bride and bride's family, this will usually be 'down payment on the house' type of sum. China's women are also increasingly well educated and themselves increasingly financially independent, meaning escalation of expectations from their would-be partner. Tough to see how to get out of this particular demographic jam
Marriage has quit appealing to young people I suppose. The policy changes to recast marriage have probably not helped - upsetting folk's view of a social institution may not help to increase participation.
Perhaps by supporting children and families, making marriage interesting and less expensive, could help? Funny nobody thinks of that.