In theory they can be mechanically, in practice high ADAS standards and functionality like regenerative breaking make it feel like a pretty high risk proposal to allow an end user in.
It doesn't take much to make a battery pack safe to work with. Every EV I've seen has contactors on both battery terminals, as well as physical shunt that is removed before servicing, in case a contactor fails closed. There's usually also contactors within the battery, making it possible to work on the battery pack itself, without any unsafe voltage present.
It's no more difficult to make safe than household wiring, and DIYers work on it all the time.
Electrically, regenerative breaking just runs the motor driver in reverse (or really, out of phase) and it doesn't take any extra components, only requiring a few instructions in the motor drivers firmware. It's not anything a DIYer has to even know exists, let alone mess with.
Driver assist has nothing to do with what type of fuel and powerplant a vehicle has, and those features can be broken by DIYers on any vehicle type. Sometimes being able to disable them is a built-in necessity for safety, for example when driving on gravel roads where they tend to do more harm than good.
Its not about the actual mechanism of regen, it's how it interacts with the other systems on the car.
Modern ADAS is a whole lot more integrated on EVs than it ever was on combustion cars, not by some inherit requirements of EVs but due to consumer demand when considering a new ev platform.
The driver is increasingly more removed, things like drive and break by wire go through a long chain of controllers in order to allow ADAS, and the input from the user is really just one more signal from a sensor.
There is no longer any circumstance where these systems are completely "off". And none were I would consider off to be safer. (Yes, even gravel and snow)
