Because we also need to replace all fossil fuels used to move things, heat things, etc.

100% renewable would require something like 10000 gigafactories to make batteries, probably not sensible. 50% means we don't need trillions of batteries.

that's assuming everyone moves to only use 2kW of energy, instead of 6 for North America and 4 for Europe. Hopefully switching to electricity will account for most of those savings.