A couple other companies tried EREVs but AFAIR one was suboptimal (Mazda had one but the motor was so small it was dangerous to use for uphill) and the other was in an expensive German thing.
Where it is challenging is that, AFAIK, a direct driveline (i.e. Honda's system) or close to (THS used by Toyota/Ford/Subaru/others), it is easier to hit a higher Gas-only MPG rating than with an EREV due to the conversion losses on each end.
And, If you compare a BYD Seal 5 DM-i to the Current Prius Prime, AFAIK if you compare euro WLTP numbers the Prime gets better MPG when it switches to gas, and has a competitive electric only range. The Seal 5 DM-I is a little bigger but close enough. The BYD certainly wins on 'price' however it is unclear how much of that is due to a truly simpler design versus labor/material input cost.