The thing about BBS-02 is, it has good torque but it's power delivery is nowhere as refined as Bosch or Impulse.
On Endless Sphere, one can read several reports of jammed chain, broken derailleurs, worn out cassettes (quicker than expected) etc. Also, 48V, 750W BBS-02 bolted onto many aluminum road/hybrid-style bikes experience much larger twisting and flex and as a result, frames are bent.
Then you start looking at steel frames and hydraulic brakes and sensors to assuage this problem. The extra cost, time and money can be considered as learning cost but not everyone wants to do that. Also, a decent system with BBS02, Hydro brakes w/ motor cutoff, RockShox suspension, XT derailleur, cassette, stiff frame etc will easily cost you $3K and at that point you're looking at a very nice Haibike which has all those but with slightly lesser torque but a solid warranty, not a china pay-return-shipping warranty.