Disclaimer: I worked at an OEM phone company. Cell towers get saturated pretty easily by crowds. Network providers probably did not account for the crowd, or e

Disclaimer: I worked at an OEM phone company. Cell towers get saturated pretty easily by crowds. Network providers probably did not account for the crowd, or even if they did, it wasn't enough. I would assume a company like Niantic asked network providers to install additional cell towers beforehand, so my best guess is they tried their best but still failed. The technical details are quite complex, and you would need to read up on GSM,UMTS,LTE,TDMA,CDMA, but the bottom-line is, the overall technology isn't good enough yet.