system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 Why do some apps stay open when you leave for 5 seconds but others take you back all the way to the starting screen?

Edit: Inspiration came from the Minecraft and Roblox app lol.
gpt
Imagine that apps are litte robots in your phone. They are all asleep in little bunk beds. When you launch an app, its robot wakes up and starts talking to you. 

When you switch to a new app, the old app’s robot now has nothing to do. On big phones, there could be room for two app robots to be awake at the same time.  On small phones, there’s only enough room for one robot at a time, so the old robot goes back to its bunk bed and goes to sleep.  Even on a big phone, the robot might get bored with no one to talk to and put itself to bed. 

When you launch the old app again, its robot wakes up, but it’s forgotten everything it was doing so it has to start all over from the beginning. 

But smart robot makers know this makes users sad!  They give their robots a litte notebook, so when they go to sleep they can write down everything they were doing.  That way, when they wake up, they can look at the notebook and remember just what to do to pick up where they left off.

It is a little more trouble for the robot maker to teach the robot how to use a notebook, but it’s so much nicer for everyone if they do.