I didn't know there was supposed to be one.

There's supposed to be one? o.o

In prior animal crossing games, your mom sent you a carnation on Mother's Day, the only way to get them.

mom doesn't love you anymore

"In New Horizons, for the entire month of May, Nook Shopping offers a unique seasonal item to celebrate Mother's Day: the Thank-you Mom mug, which costs 600 Bells."

That's all I found so far.

Ah, and it's got a carnation on it.... still, weird...