Like other big companies of all types, they want to tie you into a product ecosystem to maximise profits, bleed you dry and enslave you.
I wouldn't buy a Bafang mid-drive unless it was UART, and all of the parameters can be changed. Sadly UART is rare, because Bafang now only make CAN bus kits (according to PSWPower). If going this route,
@egroover found a UART bare motor, much searching could perhaps turn up complete UART conversion kits?
https://www.pedelecs.co.uk/forum/threads/bargains.46309/post-750593
A pricier option is to buy a CAN bus kit, sell the CAN bus controller and peripherals, replacing them with UART versions. Bear in mind even if your controller is UART, it's "Current limit" parameter might be locked/limited, though that appears to be more common on the 48V versions. Also, some 250W BBS01B motors aren't engraved "250W", so you'll need to buy or print your own for legality.