I'm pretty sure that USB wasn't created originally with charging capabilities "back in the days". Just power supply (5V @ 500mA max). Charging through USB came after and was when things started to be more complicated: someone used USB as a mean for charging a battery, then bigger batteries came, then people started to complain that devices took too long to charge, then the 500mA limit was moved, then every vendor would implement their own proprietary handshake to negotiate charging current.

> things were simple

I think USB accomplished its goal by standardizing a lot of communication protocols for a lot of (type of) devices. I lived through the 80's and 90's as a kid. I still feel the pain of plugging a new mouse or joystick and try to make it work. Then USB came and it was 'magic'.

Edit: still, if I have a serial port outputting data from a device I'm debugging and I turn on my PC, sometimes Windows would think it has a Trackball mouse connected to the serial port and will move the cursor around until I reboot my computer... I say this as a reminder on how things were back in the day (regarding communication protocols for devices).