Weird to be wondering if men are to blame here when women are typically the ones who have the final say as to when and with whom they decide to settle down and have kids with. Personally I think it is a combination of couples not wanting to have kids for a variety of reasons (not wanting to sacrifice their quality of life, lack of economic security, anxieties about the future), women delaying childbirth for longer to focus on education and career (and possibly waiting too long and not being able to have children by the time they are ready), women becoming pickier with who they choose to date and marry with the reality of hypergamy (women with higher educational and career attainment typically want to date men who are at least as successful as they are, and women are increasingly outperforming men in education and career these days). I'm sure men have some blame in this too, but most single men I know would prefer to not be single, but can't seem to find anyone interested.