With regular maintenance and replacable batteries, I don't really see any reason an average eBike wouldn't last for many years
One issue is obsolescence. The newer bikes have bigger tires, better frame designs to accommodate the motor, better controls, more battery capacity, and so forth. They are purpose built as e-bikes, rather than conventional bikes with a motor and battery strapped on.
Another is repair. Finding spare parts for the electronics is a headache. The hall sensor went out on one friend's bike motor, resulting in a new bike. Voltages and connector pinouts have to be matched unless you're a whiz with a soldering iron and can find documentation -- good luck.
Conventional bikes had similar issues with both things, but there's a brisk global market for keeping older bikes working, and a sufficient supply of aftermarket parts for obsolete bikes are available in the US. And there's a lot of shared folklore on how to keep old bikes working, along with people who cobble bikes together from old parts and sell them. I can still maintain a 1963 Schwinn. All but one of my bikes are assembled from spare parts. That kind of secondary economy hasn't emerged for e-bikes yet.
What I do hope is that otherwise good bikes and their parts don't become un-salvagable because someone can't find a wiring diagram or something like that. I hope that like with conventional bikes, a cottage industry arises that shares information and recycles out-of-fashion bikes into usable vehicles for the rest of us. What do they do with old bikes in India or Africa? That's what I want to see. I don't feel bad if that 5-10 years is followed by a decent life in someone else's hands.