Actually these laws are found in Horiot 13a:
????’ ???? ???? ???? ?????? ????? ???? ????? ????? ???? ????? ??????? ???? ???? ???? ?????? ?????? ?????? ???? ???? ????:
??’ ?”? ??? ??? ????? ???? ???? ??? ???? ???? ???? ???? ????? ??? ????? ????? ??? ???? ???? ????? ??? ??? ??? ??? ????? ?? ??? ????? ??? ?? ????? ????? ?????? ??? ???? ???? ???? ????? (????? ? ?, ??) ????? ???? (?????) [???] ??? ???? (?? ?) ???? ??????? ???’ ??? ???? ???? ????? ????? (????? ? ?, ??) ???? ???? ?? ???? ???? ???? ????? ????? ???? ???? ????? (????? ?, ?) ??? ?? ????? ???? ????? ??? ????? ???’ ???? ??????? ??? ?”? (????? ?, ?) ?? ???? ???? ??? ???? ???? ??? ???? ????? (????? ??, ?) ???? ???? ??? ?? ???? ???? ???? ????? ???? ?????? ????? ????? ????? ???? ????? ???? ???? ???? ???? ???? ‘ ???? ???? ???? ???? ???? ???? ??? ???? ???? ???? ????? ????? ???? ????? ???? ???? ??? ???? ?????? ??? ????? ??? ?? ???? ??? ???? ????? ???? ????? ???? ???? ???? ???? ??? ???? ???? ???? ??? ?? ??? ??? ?? ???? ???? ????? ?????? ??? ????? ????? ??? ????? ????? ???? ??? ???? ??? ?? ????? ???? ??? ???? ?”? ????? ??? ????? ????? ???? ?????? ???? ???? ??? ?? ???? ???? ????? ???? ????? ??? ???? ??? ??? ???? ?? ???? ???? ???? ???? ???? ????? ????? ?????? ???? ????? ???? ???? ??? ????? ?? ???? ???? ???????:
So we see that sometimes a man comes first and sometimes a woman comes first. There is also an order among men. Rambam indeed says that the reason a man is saved before a woman is that he has more mitzvot. However, according to Rashba it is a gezerat haktuv. That is to say, Hashem decided that this is the order (and there must be some order) and that is that,