Knocking Sage up is on my Bingo
Sage wants a real family, Knocking Sage without any Jade/Madame Drama is the happiest ending for Sage route. She's in final year and graduating, lost her family for the second time. Knocking and marrying Sage should be her end game.
You might say the rest of girls should be impregnable as happy endings, ehh may be Bella, but for the rest of girls no! Since most are in first year of college. (Lily, Josy, Maya can't remember rest) And getting knocked in college even with your loved one can not be a real happy ending. May be later down the line but not at this stage of life.
Other girls can have this in epilogue, but for Sage it fits even within game duration.