I'd be interested to see how many of the bikes of the last two decades are still going, my guess is the vast majority are either run down and rotting in a shed, or at the landfill. The ebike sales are at an all time high, precisely because the technology has improved immensely, but as it improves things become more proprietary, manufacturers do not want competitors to be able to reverse engineer and they also do not want consumers or unlicensed third party shops to be able to repair, following the trend of big tech brands. And sadly many of the proper good ebikes now have the entire frame designed around the motor itself, usually a mid drive one, and as such it cannot even be repurposed as a push bike. So it's just waste once the motor is gone - and it inevitably will go.
E bike conversions are far better. At least you've got a functioning bike should the motor fail, and the motors can usually be repaired - many have reverse engineered them.