Because it hasn't. I'm sure it does for some people but, because I've heard this so much, I feel inadequate that it isn't true for me.
Why do people say this? What is supposed to be easier? Or is it just about reassuring parents of small babies that this will pass, and putting a date on it makes it seem more concrete? I'm sure people meant well, of course.
Did it get easier for you after the magic 3 month mark? Or 4 months? Or ... will it only be easier when she leaves home?