Why does phone work but not Find My Iphone?

I was in a cab yesterday and I left my phone in the back seat. Within min I tried to pull up my phone on find my friends and find my iphone but I would not connect. I know the phone was on and had a high battery charge, also when I called it, it was still ringing and on. I then tried to locate it online but still nothing and both the lock and erase features are still bending but now the phone is off or dead this morning. Why was my phone not been able to be found with either of those apps but still could of been used to call?