“why not electric with a diesel motor to charge the battery when needed, diesel motor runs as optimum revs so not chucking out oodles of soot?”
The Vauxhall Ampera ran on this model (except petrol) and was a fantastic car – still the best hybrid ever built despite being designed almost 10 years ago.
Obviously they stopped building them or researching the tech further because….well just because.
The BMW i3 REX has a small petrol generator (moped engine!) but the engineering isn’t nearly as sophisticated or crucially, as robust as the Ampera despite the fancy looks.
As for petrol hybrids being more complicated – well yes and no. They do have an electric motor and batteries but as any EV driver will tell you, they aren’t the bits that go wrong very often. They don’t have a gearbox, clutch, starter motor, common rail, turbo charger etc etc and those bits tend to break on modern cars. Toyota hybrids have a pretty bombproof reliability record with many many examples of Prius going well over 200k miles with no real problems