The reasons are regulatory, not BoM costs. Getting a new medical device approved is hard, and that becomes much harder when you’ve got electronics that could hurt the user, or leave them stranded.
I'm not actually sure wheelchairs are approved as medical devices. Certainly not the same way pacemakers are. A friend of mine recently had her power chair go haywire on her and try to kill her, which sounded like a melted MOSFET from how she described the repair job. The wheelchair company apparently elected not to recall that model because it only happens to 1% of users.
If I were a wheelchair user, I'd be pissed if my government was putting in place laws that were supposed to protect me, but were in fact making my quality of life worse every day because all innovations that might make my life better were being stifled.
