I sometimes like to wave at passing cars for my daughter
That's kinda cute. Why does your daughter want you to wave at cars?
When she was young, she wanted to wave at all the passing cars while we were out and about, so we still do it today.
Waving at the cars is nice. It's good to be friendly to other people and to have fun traditions with your kids.
I just wonder why she stopped waving once she learned to talk, but we keep waving now anyway.
That is insanely adorable you try to keep little quirks like that alive and spread the joy to others! I'm sure your daughter loves all these little memories of you, and would cherish them when she's older.