Say you upgraded to the latest iPhone and stopped using your iPhone SE.
After a while, you noticed that the iPhone SE was gone and you realized that you might have accidentally donated it to a thrift store. When you got there, it wasn't there anymore, which may hint at someone already managed to snatch it.
The thing is, the phone still has a password on it and there were no sim card in there. So its pretty much useless until they get it to factory reset and got it to work like if it were still brand new and get it to work on their carrier.
Even if you could in theory managed to track it down with the help of the "Find my iPhone" function, would you care enough to try and get it back from the person who bought it? Or would you just let the be a lost cause?
Read more: https://iphoneus.org/faq/would-you-care-if-this-happened.html