There's a fundamental synergy in that electric motors get less efficient as you go faster, and internal combustion engines have their most efficient output at s

There's a fundamental synergy in that electric motors get less efficient as you go faster, and internal combustion engines have their most efficient output at significant RPMs. Using electric at low speeds and ICE at high speeds lets you use the two methods for what they're best at. The Toyota Synergy Drive design (used by many, but not all, hybrids) uses the two electric motor/generators to let the ICE run in its efficient RPM range at most speeds. There's probably more moving parts than a full EV, but it's probably less complex than a full ICE. You add one motor, but the transmission/transaxle is a whole lot simpler mechanically. And you have access to the liquid fuel network which is mature and ubiquitous. My PHEV has a two year service interval, so maintenance is not too bad. Ford had a bad batch of transmissions, and mine had to be replaced, but if they had manufactured it properly, it would have been bullet proof. The engine can be even more optimized for the efficient RPM bands it runs in, because the engine control system means it will only rarely run outside those bands.