Joseph, I strongly disagree, and I’ve been there done that. Please don’t judge others until you walk in their shoes and don’t generalize that having a career means not being interested in having a family.
Young women come home from sem, and pursue various career options – many so they can support their husbands in learning, others because it is hard to make it these days with 1 income. Those who get married young and have a family have a lot to juggle, and often do not advance in their education or careers as a result. Those who remain single have more time to continue on, but it does not mean that they are not making getting married a priority, or are totally focused on careers to the detriment of shidduchim. You make it sound like in order to get married, dating must be treated like a full time occupation, without time to do anything else on the side! One can work at a high paying job or a low paying job or go to a trade school or a graduate school and but still have time to date evenings or Sundays. For the older single, the goal is not to increase their earning potential as you suggest, but to be busy and fulfilled during a very difficult time in their lives when Hashem has decided that their fulfillment cannot come from having a family and building their own home. Some find fulfillment teaching or working with kids as a therapist, others as secretaries, and some find fulfillment as a lawyer or accountant or college professor.
On a personal note, I planned on getting married young and taking care of my kids. Hashem had other plans for me however. Without ever really planning it out, or having a specific goal in mind (afterall, for sure I would be married soon and not have the time..) I continued my education to a higher degree, and worked many years in my field until B”H I did find my BShert. Now that higher degree and work experience gives me the opportunity to work flexible hours, from home, so I can be there for my kids, and still earn enough so that my husband has been able to spend a good portion of his time learning all these years.