Why is Mai Otome considered Yuri?

[it$_aJayy:t]

I've watched mai otome and and nothing is yuri about that show except for shizuru and natsuki. And they actually don't even do anything really. All Natsuki does is blush and get jealous over the suttle things Shizuru does. Which isn't yuri. But, is that the only reason why Mai Otome and Mai Hime recieved that title? Because of Natsuki and Shizuru's extremely lowkey flirting?

If I'm missing something please do not hesitate to correct me!

domo arigato.
Thank you for clearing up the confusion!!