Why does my mum keep hassling me about making her a grandmother? (Or not making one her as the case currently stands)

My mum seems to have the opinion that the reason I’m mostly unhappy is that I’m not married & have no children. Why is this? Are married people happier? Are parents happier? Does being married or having children provide a reason for being? Any & all comments welcome.
Incidentally, my oldest brother has a son with one on the way, & my middle brother has two daughters, so it’s not like she isn’t a grandmother already…