Comment by jedbrooke

There’s a lot of good replies here but I’ll add mine too:

The simples reason is this. What you’re describing is having a gas motor spin a thing (the generator) -> charge battery -> discharge battery -> spin a thing (the wheels) to make car go. Each of those steps has efficiency losses.

That’s why most hybrids are parallel hybrids, where both the gas engine and the battery+motors can spin the wheels more or less directly, even at the same time.

you still basically get the engine spinning at a more constant rpm, and the battery kicks in for acceleration (and charges on deceleration), and now highway cruising doesn’t have any lossy conversion steps, while acceleration and braking uses the advantages of the electric drive chain.