Why can you save lives given by friends until you are ready to use them on Facebook?

Shirley-16

On mobile app you don't have to use lives right when they are given to you.  On computer if don't use lives when received they disappear.  Why?

StuckInATree

It's comes down to programming and the major drawback to running a game directly from a website on a browser as apposed to having the game app installed on your device.