A (series) hybrid car is technically the similar to a petrol car - they use the same compnents. But a hybrid is actually simpler to build, and higher performance. Why have manufacturers been concentrating on petrol-only cars for decades?
In a petrol car, the petrol engine drives the wheels and the battery charger, and the electric motor just starts the engine. In a hybrid, the motor drives the wheels and the engine only charges the battery.
This means your engine is much smaller and your motor and battery are bigger. Because an electric motor can deliver power efficiently over a high range of RPM, this also means you don’t need a carburator or gearbox, and the engine design - the difficult part of car design - is much simpler. The whole system becomes more compact, more efficient, higher performance, and cheaper.
Trains and ships have been series-hybrid for many decades. Why not cars?
Yes, true. Also, with parallel, the engine is directly driving the wheels, so you can still make use of your very sophisticated engine designs that you’ve spent the last decades perfecting. With series, you don’t need any of that complexity. Half of their engineers, their patents, their machinery, their expertise, would become redundant. That’s probably why parallel is attractive to modern manufacturers. They prefer small incremental improvements to a revolutionary leap.
There are other issues. For example parallel can give slightly more power, but is more expensive, heavier, more complex, less efficient. And I suspect parallel would have been more tricky to perfect using the technology of 50 years ago.