For whatever reason, people here, in this thread and the forums generally, gloss over two big reasons:
1. The name brand motors are designed for the European market, where speeds are capped at 15 mph. (Something like 1-5% of the market is class 3 s pedelecs, which are stifled by regulations in most places besides BE/CH.) Seems like Bafang excels with motors for higher speeds.
Personally, I know nothing about building and designing motors, but it's quite plausible that it's actually harder to make a lower speed motor work well (not long term reliability, just immediate operation), because the motor has to use a lot of finesse in giving small doses of power relative to what the human rider is putting out. If the motor is putting out 5x what you are, well, there's no finessing your way around that.
2. Big tariffs on Chinese e-bikes.
The European Union will impose duties from Saturday on Chinese electric bicycles to curb cheap imports which European producers say benefit from unfair subsidies and are flooding the market.
www.google.com
Why do people minimize these? My guess is the industry has a cozy relationship with the name brands, and saying they profit from government regulations doesn't exactly help their cause. And some people are reflexively libertarian and can't stand the thought that their precious bike industry may exploit government in service of profit.
Moreover, R&D on new bikes is expensive. Legacy bike brands already have their hands full designing bikes for actual races, where being cutting edge and winning races is a core part of their brand appeal. They'd probably rather just make an easy buck off ebikes mostly sold to old people (the prime demo in Europe, the prime market). Brands let Bosch and co do all the work, and Bosch can prevent brands from competing prices down (eg Minimum Advertised Pricing), preserving profit margins for itself and the brands. That said, prices even on Bosch bikes do seem to be coming down, and brands are putting more effort into their ebike offerings, especially Specialized, and I'm a fan of Cannondale's Class 3 Canvas 1.
That's not to say that the fancy brands aren't good, they are the gold standard. But the complete vacuum of lower end options just doesn't make sense when every product market has a range of offerings by price, but the European e-bike market... Doesn't.