Because getting over it doesn’t happen on command

From Torienne’s Characteristics of Narcissistic Mothers 
 

1. Everything she does is deniable.

In my mother’s case, she’s not quite so refined. Or maybe she’s more refined: whatever I can pinpoint is my fault, because my standards were too high or there was too much pressure on her or I didn’t support her enough. Or she blames my father.

She rarely says right out that she thinks you’re inadequate.

She compliments for being not-completely-inadequate.

She will carefully separate cause (your joy in your accomplishment) from effect (refusing to let you borrow the car to go to the awards ceremony)

Not sure what she does these days, but she used to connect joy to some negative, sinful character quality. And talk my father into seeing it the same way, and then say that HE told her punishment was in order.

It is impossible to confront someone over their tone of voice, their demeanor or they way they look at you, but once your narcissistic mother has you trained, she can promise terrible punishment without a word. As a result, you’re always afraid, always in the wrong, and can never exactly put your finger on why.

That’s pretty much true. I got a lot of flack for her general disappointment in her life.

will punish you for telling anyone else what she’s done.

Again, she’s brilliant at getting my father to dole out lashes.

She’ll slam you to other people, but will always embed her devaluing nuggets of snide gossip in protestations of concern, love and understanding (“I feel so sorry for poor Cynthia. She always seems to have such a hard time, but I just don’t know what I can do for her!”)

Omigod. So true. And she welcomes the opportunity to garner sympathy from her friends.