Why can't I find Cortana on my Phone's Google Play Store?

[AC Question]

I have a Samsung Galaxy S4. I can find it on my PC's google play store but it doesn't show up when I search for it on my phone's Google Play Store.

I want to install Cortana so that I can sync my phone with my Outlook calendar and contacts etc...

 

[hallux]

When you find it on the web version of the store (from your PC), does it say it's compatible with some of your devices? If so, click on that and it will show you a list of your devices and either a check if it's compatible or an x if it's not.