Gracie & the litterbox

This is no big deal, just something I've been curious about for a while.
Gracie, 6, always greets me at the door when I come home from work. Then, she heads straight for the litterbox. This is a daily occurence that's been going on for several years. Any thoughts, or has it just become her routine? Thanks!

I don't know if its just routine..We know cats love those..
Does Gracie use the box when you are not at home?
Perhaps she won't use it until you come home (just out of instinct...for safety reasons, I would think a cat doesn't like to be vulnerable ..or some don't anyway more than others)
Using the litter when no one is home may make Gracie feel that way..so by the time you get home, she really has to go maybe??

Just a suggestion as my Lovey won't eat when I am not there..
He is always careful about being "vulnerable to all the predators in the apartment"

I guess that's a possibility. Of my three cats, she's the most attached.