You also have to factor in that those of us in GenX and Boomers grew up not really thinking marriage was an option for us. So we didn't really date the way straight people do...then you find yourself 35 years old never having been on more than one date with anyone, and frankly, never having been in a relationship by midlife is a bit of a red flag to others, so it's a self-perpetuating cycle.
Myself I also found myself, as the single sibling with his other shit more or less together, flung into the caretaker role for two different ailing family members at times that, looking back, would have been my best shot for settling down.